Please refer to the MCQ Questions for Class 12 Physics Chapter 12 Atoms with Answers. The following Atoms Class 12 Physics MCQ Questions have been designed based on the latest syllabus and examination pattern for Class 12. Our experts have designed MCQ Questions for Class 12 Physics with Answers for all chapters in your NCERT Class 12 Physics book.

## Atoms Class 12 MCQ Questions with Answers

See below Atoms Class 12 Physics MCQ Questions, solve the questions and compare your answers with the solutions provided below.

**Question.****Doubly ionised helium atom and hydrogen ions are accelerated, from rest, through the same potential difference. The ratio of final velocities of helium and hydrogen is**

(a) 1 : √2

(b) √2 : 1

(c) 1 : 2

(d) 2 : 1

**Answer**

A

**Question.****An alpha nucleus of energy (1/2) mv ^{2} bombards a heavy nuclear target of charge Ze. Then the distance of closest approach for the alpha nucleus will be proportional to**

**Answer**

C

**Question.** 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

**Answer**

C

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

(a) because Bohr model gives in correct 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

**Answer**

A

**Question.****The energy of a hydrogen atom in the ground state is – 13.6 eV. The energy of a He ^{+} ion in the first excited state will be**

(a) –13.6 eV

(b) – 27.2 eV

(c) – 54.4 eV

(d) – 6.8 eV

**Answer**

A

**Question.****The binding energy of a H – atom, considering an electron moving around a fixed nuclei (proton), is**

**If one decides to work in a frame of reference where the electron is at rest, the proton would be moving around it. By similar arguments, the binding energy would be**

**This last expression is not correct, because**

(a) n would not be integral

(b) Bohr – quantisation applies only two electron

(c) the frame in which the electron is at rest is not inertial

(d) the motion of the proton would not be in circular orbits, even approximately.

**Answer**

C

**Question.****Ionization 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 atom according to Bohr’s theory will be**

(a) one

(b) two

(c) three

(d) four

**Answer**

C

**Question.****O _{2} molecule consists of two oxygen atoms. In the molecule, nuclear force between the nuclei of the two atoms**

(a) is not important because nuclear forces are short – ranged

(b) is as important as electrostatic force for binding the two atoms

(c) cancels the repulsive electrostatic force between the nuclei

(d) is not important because oxygen nucleus have equal number of neutrons and protons

**Answer**

A

**Question.****Given the value of Rydberg constant is 10 ^{7}m^{–1}, the wave number of the last line of the Balmer series in hydrogen spectrum will be :**

(a) 0.025 × 10

^{4}m

^{–1}

(b) 0.5 × 10

^{7}m

^{–1}

(c) 0.25 × 10

^{7}m

^{–1}

(d) 2.5 × 10

^{7 }m

^{–1}

**Answer**

C

**Question.** Two H atoms in the ground state collide inelastically. The maximum amount by which their combined kinetic energy is reduced, is

(a) 10.20 eV

(b) 20.40 eV

(c) 13.6 eV

(d) 27.2 eV

**Answer**

A

**Question.****Which of the following transitions in hydrogen atoms emit 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

**Answer**

D

**Question.** The simple Bohr 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

**Answer**

A

**Question.** An electron in hydrogen atom makes a transition n_{1} → n_{2} where n_{1 }and n_{2} are principal quantum numbers of the two states. Assuming Bohr’s model to be valid the time period of the electron in the initial state is eight times that in the final state. The possible values of n_{1 }and n_{2} are

(a) n_{1} = 4 and n_{2} = 2

(b) n_{1} = 6 and n_{2} = 2

(c) n_{1} = 8 and n_{2} = 1

(d) n_{1} = 8 and n_{2} = 2

**Answer**

A

**Question.** Two particles of masses m_{1}, m_{2} move with initial velocities u_{1} and u_{2}. On collision, one of the particles get excited to**higher level, after absorbing energy e. If final velocities of particles be v _{1} and v_{2} then we must have**

**Answer**

B

**Question.****In the spectrum of hydrogen, the ratio of the longest wavelength in the Lyman series to the longest wavelength in the Balmer series is**

(a) 9/4

(b) 27/5

(c) 5/27

(d) 4/9

**Answer**

D

**Question.** The ratio of wavelengths of the last line of Balmer series and the last line of Lyman series is :-

(a) 1

(b) 4

(c) 0.5

(d) 2

**Answer**

B

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

(a) 3

(b) 2

(c) 6

(d) 10

**Answer**

C

**Question.****When an a-particle of mass ‘m’ moving with velocity ‘v’ bombards on a heavy nucleus of charge ‘Ze’, its distance of closest approach from the nucleus depends on m as :**

(a) 1/m

(b) 1/√m

(c) 1/m^{2}

(d) m

**Answer**

A

**Question.** 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 (Plank’s Constant) = 6.6 × 10^{–34} J s]

(a) 1.46 × 10^{6} m/s

(b) 0.73 × 10^{6} m/s

(c) 3.0 × 10^{8} m/s

(d) 2.92 × 10^{6} m/s

**Answer**

A