Students must start practicing the questions from CBSE Sample Papers for Class 10 Science with Solutions Set 2 are designed as per the revised syllabus.
CBSE Sample Papers for Class 10 Science Set 2 with Solutions
Time: 3 Hours
Maximum Marks: 80
General Instructions:
- This question paper consists of 39 questions in 5 sections.
- All questions are compulsory. However, an internal choice is provided in some questions. A student is expected to attempt only one of these questions.
- Section A consists of 20 objective type questions carrying 1 mark each.
- Section B consists of 6 Very Short questions carrying 02 marks each. Answers to these questions should be in the range of 30 to 50 words.
- Section C consists of 7 Short Answer type questions carrying 03 marks each. Answers to these questions should be in the range of 50 to 80 words.
- Section D consists of 3 Long Answer type questions carrying 05 marks each. Answer to these questions should be in the range of 80 to 120 words.
- Section E consists of 3 source-based/case-based units of assessment of 04 marks each with sub-parts.
Section – A
Select and write the most appropriate option out of the four options given for each of the questions 1 – 20.
There is no negative mark for incorrect response.
Question 1.
When white light enters a glass prism from the air, the angle of deviation is maximum for:
(a) blue light
(b) yellow light
(c) red light
(d) violet light
Answer:
(d) violet light
Explanation: The angle of deviation is maximum for violet light when white light enters a glass prism from air. This is because violet light has the shortest wavelength among the colours of visible light, and it experiences the greatest amount of refraction and deviation when passing through the prism.
Question 2.
Which of the following is an example of a decomposition reaction?
(a) Burning of paper
(b) Rusting of iron
(c) Formation of water from hydrogen and oxygen
(d) Decomposition of hydrogen peroxide into water and oxygen
Answer:
(d) Decomposition of hydrogen peroxide into water and oxygen
Explanation: A decomposition reaction is a chemical reaction in which a compound breaks down into simpler substances. Hydrogen peroxide (H2O2) decomposes into water (H2O) and oxygen (O2). This reaction is commonly observed and can be catalyzed by various factors such as heat or the presence of a catalyst like manganese dioxide (MnO2). Option (a) represents a combustion reaction, option (b) represents an oxidation reaction, and option (c) represents a synthesis reaction.
Question 3.
The defect of vision in which a person cannot see the distant objects clearly but can see nearby objects clearly is called:
(a) myopia
(b) hypermetropia
(c) presbyopia
(d) bifocal eye
Answer:
(a) myopia
Explanation: A person with myopia can see nearby objects clearly but cannot see distant objects distinctly. Myopia is also known as short-sightedness.
Question 4.
Which of the following is NOT a function of the liver?
(a) Detoxification of harmful substances
(c) Regulation of blood sugar levels
(b) Production of bile for digestion
(d) Production of red blood cells
Answer:
(d) Production of red blood cells
Explanation: The liver performs numerous vital functions in the human body but is not responsible for producing red blood cells.
(a) The liver plays a crucial role in detoxifying harmful substances, such as drugs and alcohol, by breaking them down into less harmful forms that can be excreted from the body.
(b) The liver produces bile, a greenish-yellow fluid that aids in the digestion and absorption of fats in the small intestine.
(c) The liver plays a key role in maintaining blood sugar levels by storing excess glucose as glycogen and releasing it when blood sugar levels drop.
(d) Although the liver is involved in the breakdown of old or damaged red blood cells, the primary site of red blood cell production is the bone marrow, not the liver.
Understanding the liver’s functions is essential for recognizing that it does not produce red blood cells.
Question 5.
Considering the room temperature is 24°C in summer, the electrical resistance of the thermo coil, used in the AC unit is 150 Ω. Then calculate the temperature of the thermo coil if the electrical resistance is 175 Ω. Given the temperature coefficient of the thermo coil is 2.98 × 10-4 °C-1.
(a) 597°C
(b) 583°C
(c) 546°C
(d) 512°C
Answer:
(b) 583°C
Explanation:
Rt = R0 (1 + α Δ T)
175 =150 (1 + 2.98 × 10-4 Δ T)d
\(\frac{175}{150}\) – 1 = 2.98 × 10-4 × Δ T
\(\frac{25}{150}\) = 2.98 × 10-4 × Δ T
Δ T = 559.28°C
T – 24° = 559.28°C
T = 559.28°C + 24°
T = 583.28°C
Hence, the temperature of the thermo coil is 583°C.
Question 6.
Which of the following property is generally not shown by metals?
(a) Electrical conduction
(c) Dullness
(b) Sonorous in nature
(d) Ductility
Answer:
(c) Dullness
Explanation: Metals have the quality of reflecting light from their surface and can be polished. They 8 are not dull but lustrous.
Question 7.
The values of mA and μA are :
(a) 10-6 and 10-9 A respectively
(b) 10-3 and 10-6 A respectively
(c) 10-3 and 10-9 A respectively
(d) 10-6 and 10-3 A respectively
Answer:
(b) 10-3 and 10-6 A respectively
Explanation:
An ampere is the SI unit of electric current.
1A = 1000 mA or 1 mA = \(\frac{1}{1000}\) A = 10-3 A
∴ 1μA = 10-6 A
Question 8.
Name the layers of brain meninges from the inside towards the outside:
(a) Duramater, Arachnoid and Piamater
(b) Arachnoid, Duramater and Piamater
(c) Piamater, Arachnoid and Duramater
(d) Arachnoid, Piamater and Duramater
Answer:
(c) Piamater, Arachnoid and Duramater
Explanation: The brain is protected by cranial meninges, which are made up of three layers: an outside layer called duramater, a very thin middle layer called arachnoid, and an inner layer called piamater (which is in contact with the brain tissue). Thus, the layer of the brain from inside towards the outside is: Piamater, Arachnoid and Duramater.
Question 9.
If the resistance of a resistor is reduced to half of its initial value while keeping other parameters of the circuit unchanged, what will happen to the heating effects on the resistor?
(a) two times
(b) half
(c) one – fourth
(d) four times
Answer:
(a) two times
Explanation: Resistance of a resistor R Ω
The new resistance of a resistor \(\frac{\mathrm{R}}{2}\)Ω.
All other parameters of the circuit remain unchanged
Hence, the heating effect in the resistor will become two times if all other parameter of the circuit remain the same.
Question 10.
Which of the following is an advantage of sexual reproduction over asexual reproduction?
(a) Rapid population growth
(b) Greater adaptability to changing environments
(c) Production of genetically identical offspring
(d) Conservation of energy and resources
Answer:
(b) Greater adaptability to changing environments
Explanation:
(a) Asexual reproduction often leads to rapid population growth because offspring are produced without the need for a partner. However, this is not an advantage of sexual reproduction, which involves the fusion of gametes and typically has a slower reproductive rate.
(b) Sexual reproduction allows for genetic recombination, which leads to offspring with a mix of genetic traits from both parents. This diversity increases the chances of survival in changing environments. It provides a wider range of genetic variation for natural selection to act upon, enabling populations to adapt to new conditions.
(c) This statement describes a characteristic of asexual reproduction, not sexual reproduction. Asexual reproduction results in offspring that are genetically identical to the parent since they are derived from a single parent’s genetic material.
(d) Asexual reproduction is generally more efficient in terms of energy and resource conservation since it does not require the production of gametes or the search for a mating partner. Sexual reproduction, on the other hand, involves the production of specialized reproductive cells and the expenditure of energy to find and attract a mate.
Question 11.
The accumulator which is used for the domestic purpose has an electromotive force of 10 V and with an internal resistance of 0.8 Ω is externally charged by 150 V of the direct current power supply using a series resistor 18 Ω. Calculate the terminal voltage of the accumulator during use.
(a) 16.8 V
(b) 17.1V
(c) 11.3 V
(d) 15.9 V
Answer:
(d) 15.9 V
Explanation:
E = V – Ir
V = E + Ir
= 10 + (\(\frac{150-10}{18+0.8}\)) × 0.8
= 15.9V
Question 12.
Which of the following statements is not true about gene?
(a) Gene is a sequence of nucleotides.
(b) During the process of gene expression, DNA is first copied into RNA.
(c) Genes can acquire mutations in their sequence.
(d) Genes cannot acquire mutations in their sequence.
Answer:
(d) Genes cannot acquire mutations in their sequence.
Explanation: Genes can acquire mutations. A gene mutation is a change in the DNA sequence that ( makes up a permanent gene and differs from the sequence found in most people.
Question 13.
The process shown in the diagram below is:
(a) Electromagnetism
(b) Electric generator
(c) Electric Motor
(d) Electric fuse
Answer:
(a) Electromagnetism
Explanation: The diagram illustrates a basic setup of an electromagnet, which is a device that produces a magnetic field when an electric current flows through its coil. Electromagnetism is the phenomenon that describes the interaction between electricity and magnetism. When an electric current passes through the coil, it generates a magnetic field around the electromagnet, enabling it to attract or repel other magnetic objects.
Electric generator (b) is a device that converts mechanical energy into electrical energy through the principles of electromagnetic induction, typically using a rotating coil and a magnet.
Electric motor (c) is a device that converts electrical energy into mechanical energy by utilizing the interaction between the magnetic field produced by the current in the coil and an external magnetic field.
Electric fuse (d) is a safety device that protects electrical circuits from excessive current by melting a metal wire within the fuse, thus breaking the circuit.
Question 14.
Which of the following statements is NOT true regarding asexual reproduction in plants?
(a) Plants that reproduce asexually reach maturity faster than those who reproduce sexually.
(b) Plants that reproduce asexually have greater genetic diversity than those who reproduce sexually.
(c) Plants that reproduce asexually are more stable than those who reproduce sexually.
(d) Plants that reproduce asexually create offspring that are identical to the parent plant.
Answer:
(b) Plants that reproduce asexually have greater genetic diversity than those who reproduce sexually.
Explanation: Asexual reproduction in plants involves the production of offspring without the need for the fusion of gametes. Asexual reproduction allows plants to produce offspring more rapidly since they don’t need to go through the process of producing flowers, attracting pollinators, and developing seeds.
Asexual reproduction, resulting in genetic clones of the parent plant. As a result, asexual reproduction leads to limited genetic diversity among offspring, as they have identical genetic information.
Asexual reproduction provides stability in the offspring since they inherit the exact genetic traits of the parent plant. This stability can be advantageous in a stable and unchanging environment since offspring with the same genetic makeup as the parent are well-suited to their surroundings.
Question 15.
The figure below shows the Fleming’s left hand rule. Identify the correct label with the function.
(a) Thumb-force
(b) Fore finger-magnetic field
(c) Middle-finger-current
(d) All of these
Answer:
(d) All of these
Explanation: According to Fleming’s left hand rule stretch the thumb, fore finger and middle finger of your left hand side so, that they are mutually perpendicular. If the first finger points in the direction of the magnetic field and the second finger in the direction of current, then the thumb will point in the direction of force.
Question 16.
A couple has two children, one with blue eyes and the other with brown eyes. Both parents have brown
eyes. Which of the following options best explains this scenario?
(a) Eye colour follows a dominant-recessive pattern, with blue eyes being the dominant trait.
(b) Eye colour follows a dominant-recessive pattern, with brown eyes being the dominant trait.
(c) Eye colour is determined by multiple genes and is not strictly governed by a dominant-recessive pattern.
(d) Eye colour is determined solely by environmental factors and is not influenced by genetics.
Answer:
(b) Eye colour follows a dominant-recessive pattern, with brown eyes being the dominant trait.
Explanation: The inheritance of eye colour follows a more complex pattern than a simple dominant-recessive relationship. Flowever, in this specific scenario, where both parents have brown eyes and one child has blue eyes, it can be inferred that brown eyes (the trait observed in the parents) are dominant over blue eyes. This is because the child inherited a recessive allele for blue eyes from both : parents, resulting in the expression of the recessive trait.
Question No. 17 to 20 consist of two statements – Assertion (A) and Reason (R). Answer these questions selecting the appropriate option given below:
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true and R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Question 17.
Assertion: Carbon and its compounds are used as fuel.
Reason: They give a lot of heat and light when burnt in the air.
Answer:
(a) Both A and R are true and R is the correct explanation of A
Explanation: Carbon and its compounds are used as fuel for most applications because most of the carbon compounds give a lot of heat and light when burnt in the air. Saturated hydrocarbons burn with a clean flame and no smoke is produced. The carbon compounds, used as a fuel, have high calorific values.
Question 18.
Assertion: The testes descend into the scrotum just before birth.
Reason: Human males have two testes in the body.
Answer:
(b) Both A and R are true and R is not the correct explanation of A
Explanation: The descent of the testes into the scrotum just before birth is a normal physiological process. By descending into the scrotum, the testes are positioned outside the body, where the temperature is lower than inside the abdominal cavity. This temperature regulation is essential for the proper development and maturation of sperm cells, ensuring fertility and reproductive function in males.
Question 19.
Assertion: Mendel self-crossed F1 yellow with round seeds to obtain F2 generation.
Reason: F1 progeny of a yellow with round seeds and a green with wrinkled seeds are all green and wrinkled seeds.
Answer:
(c) A is true but R is false
Explanation: Mendel took two contrasting traits together for crossing i.e., the colour and shape of seeds. He chose a round yellow seed and a wrinkled green seed and crossed them. He obtained only round yellow seeds in the F1 generation. Then, F1 progeny was self-pollinated, which gave four different combinations of seeds i.e. round-yellow, wrinkled-yellow, round green and wrinkled 1 green seeds in the F2 generation.
Question 20.
Assertion: Damage to the medulla oblongata causes death.
Reason: Medulla oblongata controls involuntary functions of the body.
Answer:
(a) Both A and R are true and R is the correct explanation of A
Explanation: The medulla oblongata is a vital part of the brainstem located at the base of the brain. It is responsible for regulating various essential functions of the body, including involuntary activities such as breathing, heart rate, blood pressure, and swallowing.
Damage to the medulla oblongata can indeed be life-threatening because it disrupts the regulation of these crucial involuntary functions. As a result, it can lead to respiratory failure, cardiac arrest, or other severe complications that can be fatal.
Section – B
Question No. 21 to 26 are very short answer questions.
Question 21.
Give one difference between the corpus callosum and corpus luteum based on their function.
OR
(i) Trace the path of the sperms from where they are produced in the human body to the exterior?
(ii) Write the functions of seminal vesicles and prostate glands in human male reproductive system?
Answer:
Corpus callosum | Corpus luteum |
The corpus callosum facilitates communication and information transfer between the left and right hemispheres of the brain, enabling coordination and integration of sensory and motor functions. | The corpus luteum plays a role in the female reproductive system by producing hormones, particularly progesterone, which is essential for maintaining the uterine lining during early pregnancy. |
OR
(i) Seminiferous tubules → Epididymis → Sperm duct → Urethra This path is followed by sperm in the human body to the exterior.
(ii) Seminal vesicles secretion serves as a medium for the transportation of sperms and also, they activate and nourish the sperms. The secretion of prostate gland makes the medium alkaline and neutralises the acidic medium of the female vagina.
Question 22.
Name the plant Mendel used for his experiment. What type of progeny was obtained by Mendel in F1 and F2 generations when he crossed the tall and short plants? Write the ratio he obtained in F2 generation plants.
Answer:
Mendel used pea plant (Pisum sativum), when he crossed tall and short plants the progeny obtained in F1 generation were tall. When the F1 plants were self crossed the F2 generations showed three tall and one dwarf plant. The genotypic ratio of F2 generation is 1: 2: 1.
(TT: Tt: Tt: tt)
The phenotypic ratio is 3 :1 (Tall: Dwarf)
Question 23.
Provide examples of metals that fit the following descriptions:
(i) A metal that is in a liquid state at room temperature.
(ii) A metal that can be easily cut with a knife.
(iii) A metal that is the best conductor of heat.
(iv) A metal that is a poor conductor of heat.
Answer:
(i) Metal that exists in liquid state at room temperature is Mercury.
(ii) Metal that can be easily cut with a knife are Sodium and Potassium.
(iii) Metal that is the best conductor of heat are Silver and gold.
(iv) Metals that are poor conductors of heat are Mercury and lead.
Question 24.
How is sodium hydroxide manufactured in industries? Name the process. In this process, a gas X is formed as a by-product. This gas reacts with lime water to give a compound Y, which is used as a bleaching agent in the chemical industry. Identify X and Y and write the chemical equation of the reaction involved.
OR
A sanitary worker uses a white chemical having a strong smell of chlorine gas to disinfect the water tank:
(i) Identify the chemical compound, and write its chemical formula.
(ii) Give chemical equations for its preparation.
(iii) Write its two uses this compound other than disinfection.
Answer:
Sodium hydroxide is manufactured by the electrolysis of concentrated aqueous solution of sodium chloride.
The process of manufacture of sodium hydroxide by electrolysis process is called the chlor-alkali process. Gas X is chlorine gas and compound Y is calcium oxychloride (Bleaching powder).
OR
(i) The compound is bleaching powder and its chemical formula is CaOCl2.
(ii) Ca(OH)2 + Cl2 → CaOCl2 + H2O
(iii) (1) It is used as a bleaching agent in the textile industry.
(2) It is also used in paper industry.
Question 25.
When we increase the distance of an object from the eye, what happens to the image distance in the eye?
Answer:
For a normal eye, image distance in the eye is fixed, being equal to the distance of retina from the eye
lens. When we increase the distance of an object from the eye, the focal length of the eye lens is also increased on account of the accommodation power of the eye, to keep the image distance constant.
Question 26.
What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem?
Answer:
The increase in concentration of harmful toxic substances in the body of organisms at each trophic level of a food chain is called biological magnification. Yes, the levels of this magnification will be different at different levels of the ecosystem because the concentration of chemicals goes on increasing at different trophic levels. It is maximum at higher trophic levels and minimum at lower trophic levels. Suppose a food chain is Grass → Rabbit → Eagle, it will be the highest in eagle and minimum in grass.
Section – C
Question No. 27 to 33 are short answer questions.
Question27.
The directions of current flowing in the coil of an electromagnet at its two ends X and Y, are as shown in given figure.
(i) What is the polarity of end X ?
(ii) What is the polarity of end Y ?
(iii) Name the rule which you have used to determine the polarities.
Answer the following questions:
(i) Define electromagnetic induction.
(ii) What is a permanent magnet? Give one use of it.
(iii) How can you convert an A.C. generator in to a D.C. generator.
Answer:
(i) Since the current at end X is anticlockwise, the polarity at that end is the North pole.
(ii) Current at end Y is clockwise, hence polarity at that end is the South pole.
(iii) Clock-face rule is used to determine the polarities of the two faces of a current-carrying circular loop.
OR
(i) The production of electricity from magnetism is called electromagnetic induction.
(ii) A permanent magnet is a magnet made from steel such that once magnetized, it does not lose its magnetism easily. Permanent magnets are used in audio equipments like heaphones, loudspeakers
(iii) An A.C. generator can be converted into a D.C. generator by replacing the solid ring arrangement with split ring arrangement.
Question 28.
Briefly describe different methods of wastes disposal.
Answer:
The various methods of waste disposal are:
- Land-fills: In urban areas, wastes are filled or deposited in low lying areas. These are also known as dumping grounds where wastes are buried.
- Recycling of wastes: Some wastes, like papers, plastics, metals etc., which can be recycled are sent to special recycling treatment plants so that new substances can be made from them.
- Preparation of compost: Biodegradable wastes like kitchen wastes, peels of fruits and vegetables etc., can be used to prepare compost which serves as good manure for the plants.
- Incineration: Some wastes like medical wastes, and chemical wastes are burnt at very high temperature in an incinerator and the ashes left behind are disposed by landfills.
- Production of biogas: Biodegradable wastes can be used in biogas plants to produce biogas which is used for several purposes, like as a fuel.
Question 29.
Explain the nature of the covalent bond using the bond formation in CH3Cl.
Answer:
Carbon has 4 valence electrons. It completes its octet by sharing its four electrons with other carbon atoms or with atoms of other elements, as it can neither lose four of its electrons nor gain four electrons as both processes require extra amount of energy and would make the system unstable. Such bonds formed by sharing electrons are known as covalent bonds. In covalent bonding, both the atoms share the valence electrons, i.e., the shared electrons belong to the valence shells of both atoms.
In the formation of CH3Cl, carbon requires 4 electrons to complete its octet, while each hydrogen atom requires one electron to complete its duplet. Also, chlorine requires an electron to complete the octet.
Therefore, all of these share the electrons and as a result, carbon forms 3 bonds with hydrogen and one with chlorine.
Question 30.
While preparing a cake, baking powder is generally used. However, if your mother decides to use baking
soda instead of baking powder for the cake recipe at home.
(i) How will it affect the taste of the cake and why?
(ii) How can baking soda be converted into baking powder?
(iii) What is the role of tartaric acid added to baking soda?
Answer:
(i) Baking soda is sodium hydrogen carbonate, on heating, it is converted into sodium carbonate which is bitter in taste. Thus, if baking soda is used, the taste of the cake changes.
2NaHCO3 → Na2CO3 + H2O + CO2
(ii) Baking powder is a mixture of baking soda, cream of tartar (a dry acid), and sometimes com starch. Therefore, baking soda can be converted into baking powder by the addition of an appropriate amount of tartaric acid to it.
(iii) Tartaric acid is added to neutralise the sodium carbonate formed on heating by the decomposition of NaHCO3. If it is not added, the cake would taste bitter due to the presence of sodium carbonate in it. Also, CO2 produced during the reaction causes the cake to rise making them soft and spongy.
Question 31.
Answer the following questions:
(i) Write the electron-dot structures for sodium, oxygen, and magnesium.
(ii) Show the formation of Na2O and MgO by the transfer of electrons.
(iii) What are the ions present in these compounds Ans. (i) Electron – dot structure for Sodium (2, 8,1)
Answer:
(iii) Ions present in these compounds are Mg2+, O2- and Na+.
Question 32.
How do the guard cells regulate the opening and closing of stomatal pores?
Answer:
Guard cells are kidney shaped cells which contain thicker inner walls and thin outer walls. During day time they perform the photosynthesis process due to the presence of chloroplasts in them. When there is an increase in solute concentration inside the guard cells, water from subsidiary cells rushes inside through osmosis as a result guard cells swell up. The thin outer wall bulges out and the thick inner wall is pulled inside thus stomata opens. During night time reverse happens, water rushes out from the guard cells and they become flaccid closing the stomatal pore. Thus, turgour pressure of guard cells helps in the closing and opening of stomata.
Question 33.
Answer the following questions:
(i) What is the persistence of vision?
(ii) Define the term angle of deviation.
(iii) Define the term power of accommodation. Write the modification in the curvature of the eye lens which enables us to see the nearby objects clearly.
Answer:
(i) The image of any object formed on the retina persists for about 1/16 of a second. This continuance of sensation of an eye for sometime even after the removal of the object is called persistence of vision.
(ii) The angle between the incident ray produced forward and the emergent ray produced backward is called the angle of deviation.
(iii) The ability of the eye lens to adjust its focal length, is called the power of accommodation. There should be a contraction of ciliary muscles, that will increasing the curvature of the eye lens and becoming thicker, so the focal length of the eye lens will decrease. It will thus enable us to see the objects clearly.
Section – D
Question No. 34 to 36 are long answer questions.
Question 34.
Define a chemical reaction. State four observations which help us to determine that a chemical reaction has occused. Write one example of each of the observations with a balanced chemical equation.
OR
When two or more substances react and form some new substance, it is called a chemical reaction. As we know, all chemical reaction obeys law of chemical combination. Therefore, chemical reactions need to be balanced. It is done by hit and trial method. The chemical reactions can be classified into different types such as combination reaction, decomposition reaction, displacement reaction, double displacement reaction. The reactions take place in solution is precipitation reactions and neutralization reactions.
(i) Define a chemical reaction.
(ii) Which law is followed by all chemical reactions?
(iii) Name four types of chemical reactions.
(iv) Give an example of precipitation reactions.
Answer:
A chemical reaction is the transformation of a chemical substance into another chemical substance. Only a rearrangement of atoms takes place in a chemical reaction. Old bonds are broken, and new bonds are formed.
Some of the characteristics of chemical reactions are:
1. Change in colour: In some reactions, there is a change in colour after the reaction. For example, the chemical reaction between potassium iodide solution and lead nitrate solution is characterised by the change in colour from colourless to the appearance of yellow colour due to the formation of lead iodide.
2. Change in state: In some reactions, a change of state takes place during the reaction. The reaction might start with gaseous or liquid reactants, but end up with a solid product and vice-versa. For example: Ammonia gas reacts with hydrogen chloride gas to produce solid ammonium chloride.
NH3(g) + HCl(g) → NH4Cl (s)
3. Change in temperature: Temperature change is characteristic of many reactions. For example, the chemical reaction between quicklime and water forms slaked lime. In this reaction, the temperature of the reaction is increased due to the evolution of heat.
CaO(s) + H2O(Q) → Ca (OH)2(aq) + Heat
4. Evolution of gas: Some reactions are characterised by evolution of gas as a result of chemical reactions. For example, the chemical reaction between zinc and dilute sulphuric acid is characterised by the evolution of hydrogen gas.
Zn(s) + H2SO4(aq) → ZnS04(s) + H2(g)
OR
(i) A chemical reaction is defined as the reaction in which two or more substances react to form a new substance.
(ii) All chemical reaction follow the law of chemical combination.
(iii) Combination reactions, displacement reactions, double displacement reactions and decomposition reactions are four types of chemical reactions.
(iv) The reaction between silver nitrate and sodium chloride that forms a precipitate of silver chloride is an example of precipitation reactions.
Question 35.
What is hydrotropism? Design an experiment to demonstrate this phenomenon.
OR
The brain directs our body’s internal functions. It also integrates sensory impulses and information to form perceptions, thoughts and memories. The brain gives us self-awareness and the ability to speak and move.
(i) The brain is divided into three major subparts. Name these subparts.
(ii) Name the part of the brain, responsible for maintaining body posture?
(iii) Name the part of the brain that has the reflex centers for sneezing and vomiting?
(iv) What are meninges? What their functions?
Answer:
The movement of root of plants towards water is called hydrotropism.
Take two glass troughs, A and B, and fill each of them two-thirds with soil. In trough A plant a tiny seedling figure (a). In trough B, plant a similar seedling and place a small ‘clay pot’ inside the soil figure (b). Water the soil in trough A daily and uniformly. Do not water the soil in trough B but put some water in the clay pot buried in the soil. Leave both the troughs for a few days.
Now, carefully dig up the seedlings from both troughs without damaging their roots. We will find that the root of the seedling in trough A is straight. On the other hand, the root of seedling in trough B is found to be bent to the right side (towards the clay pot containing water) in figure (b). This can be explained as follows.
In trough A, the root of seedling gets water from both sides (because the soil is watered uniformly) in trough B, the roots gets water oozing out from the clay pot which is kept on the right side. So, the root of seedling in trough B grows and bends towards the source of water to the right side. This experiment shows that the root of a plant grows towards water. In other words, the root of a plant is positively hydrotropic.
OR
(i) The brain is divided into three main subparts: the forebrain, the midbrain and the hindbrain. The structure present towards the lower back of the skull is the hindbrain. The narrow region that links the hindbrain with the forebrain is the midbrain.
(ii) The cerebellum controls the body posture and coordinates motor activity for moving limbs.
(iii) The medulla oblongata is the region which regulates the breathing, heart rate, and blood pressure, and consists of reflex centers for sneezing, vomiting, defecating, coughing, hiccupping, and swallowing.
(iv) The brain is surrounded by three membranes, called meninges, which help to protect the brain.
Question 36.
Answer the following questions:
(i) Define the focal length of a divergent lens.
(ii) A divergent lens of focal length 30 cm forms the image of an object of size 6 cm on the same side as the object at a distance of 15 cm from its optical centre. Use the lens formula to determine the distance of the object from the lens and the size of the image formed.
(iii) Draw a ray diagram to show the formation of the image in the above situation.
OR
A students needs spectacles of power – 0.5 D for the correction of his vision.
(i) Name of defect in vision the student in suffering from.
(ii) Find the nature and focal length of the corrective lens.
(iii) List two causes of this defect.
Answer:
(i) The point from which parallel rays of light, after refraction from a lens, appear to diverge is called focus of the divergent lens, and the distance between optical centre and this focus of a divergent lens is called the focal length of divergent lens.
(ii) Focal length of the divergent lens,
f = – 30 cm
Image distance, υ = -15 cm
Object height, h1 = 6 cm
We know that, \(\frac{1}{f}=\frac{1}{υ}-\frac{1}{u}\)
or \(\frac{1}{u}=\frac{1}{υ}-\frac{1}{f}\)
OR
(i) Myopia
(ii) Concave lens with the focal length of 200 cm
Given, P = -0.5 D
We have, P = \(\frac{1}{f}\)m
f = \(\frac{1}{P}=\frac{1}{(-0.5)}\)
f = – 2m
f = – 200 cm
(iii) Two cause of Myopia are:
1. Elongation of eye ball.
2. High converging power of lens.
Section – E
Question No. 37 to 39 are case – based/data -based questions with 2 to 3 short sub – parts. Internal choice is provided in one of these sub-parts.
Question 37.
Most dirt is oily in nature and as you know, oil does not dissolve in water. The molecules of soap are sodium or potassium salts of long-chain carboxylic acids. The ionic end of soap interacts with water while the carbon chain interacts with oil. The soap molecules thus form structures called micelles where one end of the molecules is towards the oil droplet while the ionic end faces outside. This forms an emulsion in water. The soap micelle thus helps in pulling out the dirt in water and we can wash our clothes clean.
The following process is carried out:
1. Take about 10 mL of distilled water (or rain water) and 10 mL of hard water (from a tube well or hand-pump) in separate test tubes.
2. Add a couple of drops of soap solution to both.
3. Shake the test tubes vigorously for an equal period of time and observe the amount of foam formed.
4. It is observed that the quantity of foam is different in both the test tubes.
(a) What could be the reason for the difference in quantity of foam in both the test tubes?
(b) Which test tube shows less quantity of foam and why?
OR
If detergent is used in place of soap, is there any difference in the quantity of lather?
Answer:
(a) The reason for the difference in the quantity of foam in both the test tubes is the type of water sample taken in the test tubes.
(b) Test tube with hard water shows less quantity of foam because hard water contains dissolved calcium and magnesium salts. These salts react with soap to form insoluble compounds decreasing. Hence, hard water does not lather well.
OR
If detergent is used in place of soap, yes, there will be a change because the charged ends of detergents do not form insoluble precipitates with the calcium and magnesium ions in hard water. Thus, they remain effective in hard water.
Question 38.
The food material taken in during the process of nutrition is used in cells to provide energy for various life processes. Diverse organisms do this in different ways – some use oxygen to break-down glucose completely into carbon dioxide and water, some use other pathways that do not involve oxygen. In all cases, the first step is the break-down of glucose, a six-carbon molecule, into a three-carbon molecule called pyruvate. This process takes place in the cytoplasm. Further, the pyruvate may be converted into ethanol and carbon dioxide. This process takes place in yeast during fermentation. Since this process occurs in the absence of air (oxygen), it is called anaerobic respiration. Break- down of pyruvate using oxygen takes place in the mitochondria. This process breaks up the three-carbon pyruvate molecule to give three molecules of carbon dioxide. The other product is water. Since this process takes place in the presence of air (oxygen), it is called aerobic respiration.
The following process is carried out:
1. Take some freshly prepared lime water in a test tube.
2. Blow air through this lime water.
3. Note how long it takes for the lime water to turn milky.
4. Use a syringe or pichkari to pass air through some fresh lime water taken in another test tube.
5 .Note how long it takes for this lime water to turn milky.
6. It is observed that the syringe takes more time to turn lime water milky
(a) Explain why lime water turn milky instantaneously?
(b) Why syringe takes more time to turn lime water milky?
(c) Name the process through which carbon dioxide is released?
OR
Name the process in which carbon dioxide is absorbed?
Answer:
(a) Our body cells produce carbon dioxide through the oxidation of food. This gas is exhaled outside through the lungs. Lime water reacts with CO, to form an insoluble precipitate. This turns lime water milky.
(b) Syringe takes more time to turn lime water milky because the syringe push atmospheric air throv the lime water. Atmospheric air has less quantity of carbon dioxide. Therefore, it takes more time.
(c) Through the process of Respiration, carbon dioxide is released.
OR
Photosynthesis is the process by which plants use sunlight, water, and carbon dioxide to create ox and energy in sugar. Thus, in this process, carbon dioxide is absorbed.
Question 39.
In various electrical gadgets, we often use resistors in various combinations. We now, therefore intend to see how Ohm’s law can be applied to combinations of resistors. There are two methods of joining the resistors together. The resistors can be joined in series or parallel.
The arrangement of three resistors joined in series with a combination of cells (or a battery) is shown in figure below:
(a) Give a general equation for resistance connected in series.
(b) Write any one disadvantage of the series combination of resistance?
(c) Draw a schematic diagram to show resistances connected in parallel.
OR
What is the correct way to connecting the ammeter and voltmeter in the circuit to determine the equivalent resistance of two resistors in series?
Answer:
(a) When several resistors are joined in series, the resistance of the combination Rs equals the sum of their individual resistances, i.e., Rs = R1 + R2 + R3
(b) In a series circuit the current is constant throughout the electric circuit. Thus, it is obviously impracticable to connect an electric bulb and an electric heater in series, because they need currents of widely different values to operate properly.
(d) The correct way of connecting the ammeter and voltmeter in the circuit to determine the equivalent resistance of two resistors is by connecting the ammeter in series and the voltmeter in parallel. Ammeter is connected in series, so that whole current passes through it, and the voltmeter is connected in parallel to so that it can measure the complete voltage of the circuit.