# MCQs for Physics Class 12 with Answers Chapter 12 Atoms

Students of class 12 Physics should refer to MCQ Questions Class 12 Physics Atoms with answers provided here which is an important chapter in Class 12 Physics NCERT textbook. These MCQ for Class 12 Physics with Answers have been prepared based on the latest CBSE and NCERT syllabus and examination guidelines for Class 12 Physics. The following MCQs can help you to practice and get better marks in the upcoming class 12 Physics examination

**Chapter 12 Atoms MCQ with Answers Class 12 Physics**

MCQ Questions Class 12 Physics Atoms provided below have been prepared by expert teachers of grade 12. These objective questions with solutions are expected to come in the upcoming Standard 12 examinations. Learn the below provided MCQ questions to get better marks in examinations.

**Question. The size of the atom is proportional to**

(a) A

(b) A ^{1/3}

(c) A ^{2/3}

(d) A^{ –1/3}

**Answer**

B

** Question. The ratio of energies of the hydrogen atom in its first to second excited state is**

(a) 1 : 4

(b) 4 : 1

(c) – 4 : – 9

(d) – (1/4) : (1/9)

**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.** To explain his theory, Bohr used

(a) conservation of linear momentum

(b) quantisation of angular momentum

(c) conservation of quantum

(d) none of these

**Answer**

B

**Question.** The wavelength of the first line of Lyman series in hydrogen is 1216 Å. The wavelength of the second line of the same series will be

(a) 912 Å

(b) 1026 Å

(c) 3648 Å

(d) 6566 Å

**Answer**

B

**Question.** Taking the Bohr radius as a0 = 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.** 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.** 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.****In the following transitions of the hydrogen atom, the one which gives an absorption line of highest frequency is**

(a) n = 1 to n = 2

(b) n = 3 to n = 8

(c) n = 2 to n = 1

(d) n = 8 to n = 3

**Answer**

A

**Question.****When an electron in an atom goes from a lower to a higher orbit, its **(a) kinetic energy (KE) increases, potential energy (PE) decreases

(b) KE increases, PE increases

(c) KE decreases, PE increases

(d) KE decreases, PE decreases

**Answer**

C

**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) 0.25 × 107 m^{–1}

(b) 2.5 × 107 m^{–1}

(c) 0.025 × 104 m^{–1}

(d) 0.5 × 107 m^{–1}

**Answer**

A

**Question.** If an electron in a hydrogen atom jumps from the 3rd orbit to the 2nd orbit, it emits a photon of wavelength λ. When it jumps from the 4th orbit to the 3rd orbit, the corresponding wavelength of the photon will be

**Answer**

C

**Question.** The Bohr model for the spectra of a H-atom

(a) will not be applicable to hydrogen in the molecular from.

(b) will not be applicable as it is for a He-atom.

(c) is valid only at room temperature.

(d) predicts continuous as well as discrete spectral lines.

**Answer**

A, B

**Question.** According to Bohr’s theory, the energy of radiation in the transition from the third excited state to the first excited state for a hydrogen atom is

(a) 0.85 eV

(b) 13.6 eV

(c) 2.55 eV

(d) 3.4 eV

**Answer**

C

**Question.****A set of atoms in an excited state decays.**

(a) in general to any of the states with lower energy.

(b) into a lower state only when excited by an external electric field.

(c) all together simultaneously into a lower state.

(d) to emit photons only when they collide.

**Answer**

A

**Question.** The ratio of the speed of the electrons in the ground state of hydrogen to the speed of light in vacuum is

(a) 1/2

(b) 2/237

(c) 1/137

(d) 1/237

**Answer**

C

**Question. The following statements are all true. Which one did Rutherford consider to be supported by the results of experiments in which a-particles were scattered by gold foil?**

(a) The nucleus of an atom is held together by forces which are much stronger than electrical or gravitational forces.

(b) The force of repulsion between an atomic nucleus and an a-particle varies with distance according to inverse square law.

(c) a-particles are nuclei of Helium atoms.

(d) Atoms can exist with a series of discrete energy levels.

**Answer**

B

**Question. The angular speed of the electron in the nth orbit of Bohr hydrogen atom is**

(a) directly proportional to n

(b) inversely proportional to √n

(c) inversely proportional to n^{2}

(d) inversely proportional to n^{3}

**Answer**

D

**Question. As the quantum number increases, the difference of energy between consecutive energy levels**

(a) remain the same

(b) increases

(c) decreases

(d) sometimes increases and sometimes decreases.

**Answer**

C

**Question. For the principal quantum number n = 4, the total number of different possible values of the azimuthal quantum number l, is**

(a) 2

(b) 8

(c) 4

(d) 3

**Answer**

C

**Question. According to the Bohr theory of H-atom, the speed of the electron, its energy and the radius of its orbit varies with the principal quantum number n, respectively, as**

**Answer**

D

**Question. With increasing quantum number, the energy difference between adjacent energy levels in atoms**

(a) decreases

(b) increases

(c) remains constant

(d) decreases for low Z and increases for high Z

**Answer**

A

**Question. In a hydrogen atom following the Bohr’s postulates the product of linear momentum and angular momentum is proportional to (n) ^{x} where ‘n’ is the orbit number. Then ‘x’ is**

(a) 0

(b) 2

(c) –2

(d) 1

**Answer**

A

**Question. Line spectrum is obtained whenever the incandescent vapours at low pressure of the excited substance are in their**

(a) atomic state

(b) molecular state

(c) nuclear state

(d) None of these

**Answer**

A

**Question. In an atom, the two electrons move round the nucleus in circular orbits of radii R and 4R. The ratio of the time taken by them to complete one revolution is**

(a) 1/4

(b) 4/1

(c) 8/1

(d) 1/8

**Answer**

D

**Question. According to Bohr’s model of hydrogen atom**

(a) the linear velocity of the electron is quantised.

(b) the angular velocity of the electron is quantised.

(c) the linear momentum of the electron is quantised.

(d) the angular momentum of the electron is quantised.

**Answer**

D

**Question. The ratio of the energies of the hydrogen atom in its first to second excited states is**

(a) 1/4

(b) 4/9

(c) 9/4

(d) 4

**Answer**

C

**Question. The angular momentum of the electron in hydrogen atom in the ground state is**

(a) 2h

(b) h/2

(c) h/2π

(d) h/4π

**Answer**

C

**Question. In which of the following series, does the 121.5 nm line of the spectrum of the hydrogen atom lie ?**

(a) Lyman series

(b) Balmer series

(c) Paschen series

(d) Brackett series.

**Answer**

A

**Question. According to classical theory, the circular path of an electron in Rutherford atom is**

(a) spiral

(b) circular

(c) parabolic

(d) straight line

**Answer**

A

**Question. The angular momentum of electron in n ^{th} orbit is given by**

(a) nh

(b) h/2πn

(c) n(h/2π)

(d) n

^{2}(h/2π)

**Answer**

C

**Question. The kinetic energy of the electorn in an orbit of radius r in hydrogen atom is (e = electronic charge)**

(a) e^{2}/r^{2}

(b) e^{2}/2r

(c) e^{2}/r

(d) e^{2}/2r^{2}

**Answer**

B

**Question. A 15.0 eV photon collides with and ionizes a hydrogen** **atom. If the atom was originally in the ground state****(ionization potential =13.6 eV), what is the kinetic energy of the ejected electron?**

(a) 1.4 eV

(b) 13.6 eV

(c) 15.0 eV

(d) 28.6 eV

**Answer**

A

**Question.** **5. Energy levels, A, B, C of a certain atom correspond to increasing values of energy i.e. E _{A} < E_{B} < E_{C.} If λ_{1}, λ_{2}, λ_{3 }are the wavelengths of radiations corresponding to the transitions C to B, B to A and C to A respectively, which of the following relations is correct ?**

**Answer**

B

**Question.** **In Bohr’s model of the hydrogen atom, let R, V, T and E represent the radius of the orbit, speed of the electron, time period of revolution of electron and the total energy of the electron respectively. The quantity proportional to the quantum number n is**

(a) VR

(b) E

(c) r

(d) T

**Answer**

A

**Question. In a hypothetical Bohr hydrogen atom, the mass of the electron is doubled. The energy ‘ E _{0} and radius ‘ r_{0} of the first orbit will be (r_{0} is the Bohr radius)**

(a) –11.2 eV

(b) –6.8 eV

(c) –13.6 eV

(d) –27.2 eV

**Answer**

D

**Question.** **Let n _{1 }be the frequency of the series limit of the Lyman series, n_{2} be the frequency of the first line of the Lyman series, and n_{3} be the frequency of the series limit of the Balmer series.**

**Answer**

A

**Question. Which of the following series in the spectrum of hydrogen atom lies in the visible region of the electromagnetic spectrum?**

(a) Paschen series

(b) Balmer series

(c) Lyman series

(d) Brackett series

**Answer**

B

**Question.** **The proof of quantization of energy states in an atom is obtained by the experiment performed by**

(a) Thomson

(b) Millikan

(c) Rutherford

(d) Franck and Hertz

**Answer**

D

**Question. The approximate value of quantum number n for the circular orbit of hydrogen 0.0001 mm in diameter is**

(a) 1000

(b) 60

(c) 10000

(d) 31

**Answer**

D

**Question. The ratio of maximum to minimum wavelength in Balmer series is**

(a) 3 : 4

(b) 1 : 4

(c) 5 : 36

(d) 5 : 9

**Answer**

D

**Question.. The extreme wavelengths of Paschen series are**

(a) 0.365 mm and 0.565 mm

(b) 0.818 mm and 1.89 mm

(c) 1.45 mm and 4.04 mm

(d) 2.27 mm and 7.43 mm

**Answer**

B

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

(a) 4

(b) 3

(c) 1

(d) 2

**Answer**

B

**Question. The energy levels of the hydrogen spectrum is shown in figure. There are some transitions A, B, C, D and E. Transition A, B and C respectively represent**

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

(b) ionization potential of hydrogen, second spectral line of Balmer series, third spectral line of Paschen series

(c) series limit of Lyman series, third spectral line of Balmer series and second spectral line of Paschen series

(d) series limit of Lyman series, second spectral line of Balmer series and third spectral line of Paschen series

**Answer**

C

**Question. The ratio of the longest to shortest wavelengths in Brackett series of hydrogen spectra is**

**Answer**

A

**Question. Which of the following statements are true regarding Bohr’s model of hydrogen atom?**

(I) Orbiting speed of electron decreases as it shifts to discrete orbits away from the nucleus

(II) Radii of allowed orbits of electron are proportional to the principal quantum number

(III) Frequency with which electrons orbit around the nucleus in discrete orbits is inversely proportional to the cube of principal quantum number

(IV) Binding force with which the electron is bound to the nucleus increases as it shifts to outer orbits Select correct answer using the codes given below.**Codes :**

(a) I and II

(b) II and IV

(c) I, II and III

(d) II, III and IV

**Answer**

A

**Question. Electrons in a certain energy level n = n _{1}, can emit 3 spectral lines. When they are in another energy level, n = n_{2}. They can emit 6 spectral lines. The orbital speed of the electrons in the two orbits are in the ratio of**

(a) 4 : 3

(b) 3 : 4

(c) 2 : 1

(d) 1 : 2

**Answer**

A

**Fill in the Blanks**

**Question. The angle of scattering q for zero value of impact parameter b is _________________.**

**Answer**

180°

**Question. _______________ is the ionisation potential of hydrogen atom.**

**Answer**

13.6 eV

**Question. The force responsible for scattering of alpha particle with target nucleus is _______________.**

**Answer**

electrostatic force

**Question. _______________ is a physical quantity whose dimensions are the same as that of Plank’s constant.**

**Answer**

Angular momentum

**Question. When an electron jumps from 2nd stationary orbit of hydrogen atom to 1st stationary orbit, the energy emitted is _________________.**

**Answer**

2 eV

**Question. The frequency spectrum of radiation emitted as per Rutherford’s model of atom is _____________.**

**Answer**

continuous

**Question. Total energy of electron in a stationary orbit is _________________, which means the electron is bound to the nucleus and is not free to leave it.**

**Answer**

negative

**Question. _______________ series of hydrogen spectrum lies in the visible region electromagnetic spectrum.**

**Answer**

Balmer

**Question. According to de Broglie a stationary orbit is that which contains an _______________ number of de Broglie waves associated with the revolting electron.**

**Answer**

integral

**Question. The value of Rydberg constant is _________________.**

**Answer**

1.09 × 107 m–1

We hope the above multiple choice questions for Class 12 Physics for Chapter 12 Atoms provided above with answers based on the latest syllabus and examination guidelines issued by CBSE, NCERT and KVS are really useful for you. Atoms is an important chapter in Class 12 as it provides very strong understanding about this topic. Students should go through the answers provided for the MCQs after they have themselves solved the questions. All MCQs have been provided with four options for the students to solve. These questions are really useful for benefit of class 12 students. Please go through these and let us know if you have any feedback in the comments section.