Contents

**NEET Physics Chapter Wise Mock Test – Atoms and Nuclei**

**Question 1:
**An α-particle after passing through a potential difference of V volt collides with a nucleus. If the atomic number of the nucleus is Z, then the distance of closest approach is

(a) 14.4(Z/V) Å

(b) 14.4(Z/V) m

(c) 14.4(V/Z) Å

(d) 14.4(V/Z) m

**Question 2:
**In Rutherford scattering experiment, the number of α-particles scattered at 60° is 5 x10

^{6}. The number of α-particles scattered at 120° will be

(a) 15 x10

^{6}

(b) 3/5 x10

^{6}

(c) 5/9 x10

^{6}

(d) None of these

**Question 3:
**The total energy of electron in the ground state of hydrogen atom is -13.6 eV. The kinetic energy of an electron in the first excited state is

(a) 3.4 eV

(b) 6.8 eV

(c) 13.6eV

(d) 1.7 eV

**Question 4:
**Taking the Bohr radius as a

_{0}= 53 pm, the radius of Li

^{++}ion in its ground state, on the basis of Bohr’s model, will be about

(a) 53 pm

(b) 27 pm

(c) 18 pm

(d) 13 pm

**Question 5:
**

**Question 6:
**For the ground state, the electron in the H-atom has an angular momentum=h, according to the simple Bohr’s model. Angular momentum is a vector and hence, there will be infinitely many orbits with the vector pointing in all possible directions. In actually, this is not true

(a) because Bohr’s model gives incorrect values of angular momentum

(b) because only one of these would have a minimum energy

(c) angular momentum must be in the direction of spin of electron

(d) because electrons go around only in horizontal orbits

**Question 7:
**How many revolutions does an electron complete in one second in the first orbit of hydrogen atom?

(a) 675 x10

^{15}

(b) 100

(c) 1000

(d) 1

**Question 8:
**The total energy of an electron in the first excited state of hydrogen is about -3.4 eV. Its kinetic energy in this state is

(a) -3.4 eV

(b) -6.8 eV

(c) 6.8 eV

(d) 3.4 eV

**Question 9:
**The ratio of nuclear radii of the gold isotope 79Au

^{197}and the silver isotope 47Ag

^{107}is

(a) 0.233

(b) 2.33

(c) 1.225

(d) 12.25

**Question 10:
**Monochromatic radiation of wavelength λ is incident on a hydrogen sample. In ground state, hydrogen atom absorbs a fraction of light and subsequently emits radiation of six different wavelengths. The wavelength λ is

(a) 97.5nm

(b) 121.6nm

(c) 110.3nm

(d) 45.2nm

**Question 11:
**Given that, R is Rydberg’s constant. When an electron in an atom of hydrogen jumps from an outer orbit n=3 to an inner orbit n=2, the wavelength of emitted radiations will be equal to

(a) R/6

^{2}

(b) 6

^{2}/R

(c) 5R/36

(d) 36/5R

**Question 12:
**The limit of Balmer series is 3646Å. The wavelength of first member of this series will be

(a) 6563Å

(b) 3646Å

(c) 7200Å

(d) 1000Å

**Question 13:
**

**Question 14:
**A hydrogen like atom emits radiations of frequency 2.7x 10

^{15}Hz when it makes a transition from n=2 to n=1. The frequency emitted in a transition from n=3 to n=1 will be

(a) 1.6 x 10

^{15}Hz

(b) 3.2 x 10

^{15}Hz

(c) 4.8 x 10

^{15}Hz

(d) 6.4 x 10

^{15}Hz

**Question 15:
**The recoil speed of hydrogen atom after it emits a photon in going from n=5 state to n=1 state is (Given, R

_{∞}=1.097 x10

^{7}m

^{-1}, h = 6.63 x10

^{-34}Js, M

_{H}= 1.67x 10

^{-27}kg)

(a) 2.2 ms

^{-1}

(b) 4.18 ms

^{-1}

(c) 6.2 ms

^{-1}

(d) 1 ms

^{-1}

**Question 16:
**In a special experiment angular momentum is an even integral multiple of h/2π. The longest possible wavelength emitted by hydrogen in visible region in the experiment according to Bohr’s model will be

(a) 478nm

(b) 322nm

(c) 33nm

(d) 50nm

**Question 17:
**The wavelength of radiation emitted is λ

_{0}when an electron jumps from the third to second orbit of hydrogen atom. For the electron jump from fourth to the second orbit of the hydrogen atom, the wavelength of radiation emitted will be

(a) (16/25) λ

_{0}

(b) (20/27) λ

_{0}

(c) (27/20) λ

_{0}

(d) (25/16) λ

_{0}

**Question 18:
**When an electron jumps from a level n=4 to n=1, momentum of the recoiled hydrogen atom will be

(a) 6.8 x 10

^{-27}kg-ms

^{-1}

(b) 12.75×10

^{-19}kg-ms

^{-1}

(c) 136×10

^{-19}kg-ms

^{-1}

**(d) zero**

**Question 19:
**Which of the following transition in hydrogen atoms limit photons of highest frequency?

(a) n=1 to n=2

(b) n=2 to n=6

(c) n=6 to n=2

(d) n=2 to n=1

**Question 20:
**A hydrogen atom moves with velocity u and makes head on inelastic collision with another stationary H-atom. Both atoms are in ground state before collision. The minimum value of u, if one of the them is to be given a minimum excitation energy is

(a) 2.64 x 10

^{4}ms

^{-1}

(b) 6.24 x 10

^{4}ms

^{-1}

(c) 2.64 x 10

^{8}ms

^{-1}

(d) 6.24 x 10

^{8}ms

^{-1}

**Question 21:
**The energy required to excite an electron from n=2 to n=3 energy state is 47.2 eV. The charge number of the nucleus, around which the electron is revolving, will be

(a) 5

(b) 10

(c) 15

(d) 20

**Question 22:
**The ratio of minimum wavelengths of Lyman and Balmer series will be

(a) 1.25

(b) 0.25

(c) 5

(d) 10

**Question 23:
**Ionisation potential of hydrogen atom is 13.6 eV. Hydrogen atoms in the ground state are excited by monochromatic radiation of photon energy 12.1 eV. The spectral lines emitted by hydrogen atoms according to Bohr’s theory will be

(a) one

(b) two

(c) three

(d) four

**Question 24:
**The energy of an electron in nth orbit of hydrogen atom is -13.6/n

^{2}eV. Energy required to excite the electron from the first orbit to the third orbit is

(a) 10.2 J

(b) 12.09 J

(c) 12.09 eV

(d) 13.6 eV

**Question 25:
**The total energy of the electron orbiting around the nucleus in the ground state of the atom is

(a) less than zero

(b) zero

(c) more than zero

(d) sometimes less and sometimes more than zero

**Question 26:
**

**Direction (Q.NOs. 27-31):** In each of the following questions a statement of Assertion is given followed by a corresponding statement of Reason just below it. Of the statements mark the correct answer as

(a) If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion

(b) If both Assertion and Reason are true but the Reason is not correct explanation of the Assertion

(c) If Assertion is true but Reason is false

(d) If both Assertion and Reason are false

**Question 27:
Assertion (A): **An α-particle is a doubly ionised helium atom.

**An α-particle carries 2 units of positive charge.**

Reason (R):

Reason (R):

**Question 28:
Assertion (A): **Bohr had to postulate that the electrons in stationary orbits around the nucleus do not radiate.

**According to classical physics, all moving electrons radiate.**

Reason (R):

Reason (R):

**Question 29:
Assertion (A): **In He-Ne laser, population inversion takes place between energy levels of neon atoms.

**Helium atoms have a meta-stable energy level.**

Reason (R):

Reason (R):

**Question 30:
Assertion (A): **The different lines of emission spectra (like Lyman, Balmer etc.) of atomic hydrogen gas are produced by different atoms.

**The sample of atomic hydrogen- gas consists of millions of atoms.**

Reason (R):

Reason (R):

**Question 31:
Assertion (A): **It is difficult to excite nucleus to higher energy states by usual methods which we use to excite atoms like by heating or by irradiation of light.

**Terms like ground state or excited state for nucleus are meaningless.**

Reason (R):

Reason (R):

**Question 32:
**The simple Bohr’s model cannot be directly applied to calculate the energy levels of an atom with many electrons. This is because

(a) of the electrons not being subject to a central force

(b) of the electrons colliding with each other

(c) of screening effects

(d) the force between the nucleus and an electron will no longer be given by Coulomb’s law

**Question 33:
**Consider 3

^{rd}orbit of He

^{+}(Helium), using non-relativistic approach, the speed of electron in this orbit will be [given, K=9×10

^{9}constant, Z=2 and h (Planck constant)=6.6 x 10

^{-34}Js]

(a) 2.92 x 10

^{6}m/s

(b) 1.46 x 10

^{6}m/s

(c) 0.73 x 10

^{6}m/s

(d) 3.0 x 10

^{8}m/s

**Question 34:
**Hydrogen atom in ground state is excited by a monochromatic radiation of λ = 975Å. Number of spectral lines in the resulting spectrum emitted will be

(a) 3

(b) 2

(c) 6

(d) 10

**Question 35:
**Outside a nucleus

(a) neutron is stable

(b) neutron is unstable

(c) proton and neutron both are stabie

(d) proton and neutron both are unstable

**Question 36:
**The mother and daughter elements, with the emission of γ-rays are

(a) isotopes

(b) isobars

(c) isomers

(d) isodiapheres

**Question 37:
**Energy E of a hydrogen atom with principal quantum number n is given by E=13.6/n

^{2}eV. The energy of a photon ejected when the electron jumps from n=3 state to n=2 state of hydrogen is approximately

(a) 1.5 eV

(b) 0.85 eV

(c) 3.3 eV

(d) 1.9 eV

**Question 38:
**The existence of a positively charged nucleus in an atom was first suggested by the experiment of

(a) J J Thomson

(b) E Rutherford

(c) Chadwick

(d) Hahn and Strassman

**Question 39:
**In the lowest energy level of hydrogen atom, the electron has the angular momentum

(a) π/h

(b) h/π

(c) h/2π

(d) 2π/h

**Question 40:
**According to Bohr’s theory (assuming infinite mass of the nucleus), the frequency of the second line of the Balmer series is

(a) 6.16 x 10

^{14}Hz

(b) 6.16 X 10

^{10}Hz

(c) 6.16x 10

^{13}Hz

(d) 6.16x 10

^{16}Hz

**Question 41:
Assertion (A):** Balmer series lies in the visible region of electromagnetic spectrum.

**(a) If both assertion and reason are true and reason is the correct explanation of assertion**

(b) If both assertion and reason are true but the reason is not the correct explanation of assertion

(c) If assertion is true but reason is false

(d) If both assertion and reason are false

**Question 42:
**The ionisation potential of hydrogen atom is 13.6 eV. The energy required to remove an electron from the second orbit of hydrogen will be

(a) 27.4 eV

(b) 13.6 eV

(c) 3.4 eV

(d) None of these

**Question 43:
**Monochromatic radiation emitted when electron on hydrogen atom jumps from first excited to the ground state irradiates a photosensitive material. The stopping potential is measured to be 3.57 V. The threshold frequency of the material is

(a) 4×10

^{15}Hz

(b) 5×10

^{15}Hz

(c) 1.6×10

^{15}Hz

(d) 2.5×10

^{15}Hz

**Question 44:
**Electron in hydrogen atom first jumps from third excited state to second excited state and then from second excited to the first excited state. The ratio of the wavelengths λ

_{1}: λ

_{2}emitted in the two cases is

(a) 7/5

(b) 27/ 20

(c) 27/5

(d) 20/ 7

**Question 45:
**An electron of a stationary hydrogen atom passes from the fifth energy level to the ground level. The velocity that the atom acquired as a result of photon emission will be

(a) 24hR/25m

(b) 25hR/24m

(c) 24m/25hR

(d) 25m/24hR

(m is the mass of the electron, R=Rydberg constant and h=Planck constant).

**Question 46:
**Hydrogen atom excites energy level from fundamental state to n=3. Number of spectrum lines according to Bohr is

(a) 4

(b) 3

(c) 1

(d) 2

**Question 47:
**The wavelength of the first line of Lyman series for hydrogen atom is equal to that of the second line of Balmer series for a hydrogen like ion. The atomic number Z of hydrogen like ion is

(a) 2

(b) 3

(c) 4

(d) 5

**Question 48:
**An electron jumps from the 4th orbit to 2nd orbit of hydrogen atom. Given the Rydberg’s constant R=10

^{5}cm

^{-1}the frequency in hertz of the emitted radiation will be

(a) 3/16 x 10

^{5}

(b) 3/16 x 10

^{15}

(c) 9/16 x 10

^{15}

(d) 3/4 x 10

^{15}

**Question 49:
**In figure, the energy levels of the hydrogen atom have been shown along with some transitions marked A, B and C. The transitions A, B and C respectively, represents

**(a) the first member of the Lyman series, third member of Balmer series and second member of Paschen series**

(b) the ionisation potential of H, second member of Balmer series and third member of Paschen series

(c) the series limit of Lyman series, second member of Balmer series and second member of Paschen series

(d) the series limit of Lyman series, third member of Balmer series and second member of Paschen series

### Answers:

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