CBSE Class 12 Physics Atoms MCQs Set C

Question. The total energy of an electron in an atom in an orbit is – 3.4 eV. Its kinetic and potential energies are, respectively
(a) 3.4 eV, 3.4 eV
(b) – 3.4 eV, – 3.4 eV
(c) – 3.4 eV, – 6.8 eV
(d) 3.4 eV, – 6.8 eV

Answer : D

Question. The radius of the first permitted Bohr orbit for the electron, in a hydrogen atom equals 0.51 Å and its ground state energy equals –13.6 eV. If the electron in the hydrogen atom is replaced by muon (m–) [charge same as electron and mass 207 me], the first Bohr radius and ground state energy will be
(a) 0.53 × 10^–13 m, –3.6 eV
(b) 25.6 × 10^–13 m, –2.8 eV
(c) 2.56 × 10^–13 m, –2.8 keV
(d) 2.56 × 10^–13 m, –13.6 eV 

Answer : C

Question. The ratio of kinetic energy to the total energy of an electron in a Bohr orbit of the hydrogen atom, is
(a) 1 : 1
(b) 1 : –1
(c) 2 : –1
(d) 1 : –2

Answer : B

Question. Consider 3rd orbit of He+ (Helium), using non-relativistic approach, the speed of electron in this orbit will be [given K = 9 × 109 constant, Z = 2 and h (Planck’s constant) = 6.6 × 10^–34 J s]
(a) 0.73 × 10⁶ m/s
(b) 3.0 × 10⁸ m/s
(c) 2.92 × 10⁶ m/s
(d) 1.46 × 10⁶ m/s

Answer : D

Question. The energy of the ground electronic state of hydrogen atom is –13.6 eV. The energy of the first excited state will be
(a) –27.2 eV
(b) –52.4 eV
(c) –3.4 eV
(d) –6.8 eV

Answer : C

Question. When hydrogen atom is in its first excited level, its radius is ………. of the Bohr radius.
(a) twice
(b) 4 times
(c) same
(d) half

Answer : B

Question. According to Bohr’s principle, the relation between principal quantum number (n) and radius of orbit (r) is
(a) r ∝ 1/n
(b) r ∝ 1/n²
(c) r ∝ n
(d) r ∝ n₂

Answer : D

Question. In a Rutherford experiment, the number of particles scattered at 90° angle are 28 per minute then number of scattered particles at an angle 60° and 120° will be
(a) 117 per minute, 25 per minute
(b) 50 per minute, 12.5 per minute
(c) 100 per minute, 200 per minute
(d) 112 per minute, 12.4 per minute

Answer : D

Question. 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 l1 : l2 emitted in the two cases is
(a) 7/5
(b) 27/20
(c) 27/5
(d) 20/7

Answer : D

Question. 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) 25m/24hR
(d) 24m/25hR
(m is the mass of the electron, R Rydberg constant and h Planck’s constant)

Answer : A

Question. The transition from the state n = 3 to n = 1 in a hydrogen like atom results in ultraviolet radiation.
Infrared radiation will be obtained in the transition from
(a) 2 → 1
(b) 3 → 2
(c) 4 → 2
(d) 4 → 3

Answer : D

Question. A hydrogen atom in its ground state absorbs 10.2 eV of energy. The orbital angular momentum is increased by
(a) 1.05 × 10^–34 J-s
(b) 3.16 × 10^–34 J-s
(c) 2.11 × 10^–34 J-s
(d) 4.22 × 10^–34 J-s

Answer : A

Question. The ionization energy of Li⁺⁺ is equal to
(a) 9hcR
(b) 6hcR
(c) 2hcR
(d) hcR.

Answer : A

Question. The Rutherford a-particle experiment shows that most of the a-particles pass through almost unscattered while some are scattered through large angles. What information does it give about the structure of the atom?
(a) Atom is hollow.
(b) The whole mass of the atom is concentrated in a small centre called nucleus
(c) Nucleus is positively charged
(d) All of the options

Answer : D

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 Bohr model of atoms
(a) Assumes that the angular momentum of electrons is quantized.
(b) Uses Einstein’s photoelectric equation.
(c) Predicts continuous emission spectra for atoms.
(d) Predicts the same emission spectra for all types of atoms.

Answer : A

Question. The ground state energy of H-atom is –13.6 eV. The energy needed to ionize H-atom from its second excited state
(a) 1.51 eV
(b) 3.4 eV
(c) 13.6 eV
(d) none of these

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 l. When it jumps from the 4th orbit to the 3rd orbit, the corresponding wavelength of the photon will be
(a) 16/25λ
(b) 9/16λ
(c) 20/7λ
(d) 20/13λ

Answer : C

Question. Hydrogen atom in ground state is excited by a monochromatic radiation of l = 975 Å. Number of spectral lines in the resulting spectrum emitted will be
(a) 3
(b) 2
(c) 6
(d) 10

Answer : C

Question. Taking Rydberg’s constant R_H = 1.097 × 10⁷m, first and second wavelength of Balmer series in hydrogen spectrum is
(a) 2000 Å, 3000 Å
(b) 1575 Å, 2960 Å
(c) 6529 Å, 4280 Å
(d) 6552 Å, 4863 Å

Answer : B

Question. In which of the following systems will the radius of the first orbit (n = 1) be minimum?
(a) doubly ionized lithium
(b) singly ionized helium
(c) deuterium atom
(d) hydrogen atom

Answer : A

Question. The third line of Balmer series of an ion equivalnet to hydrogen atom has wavelength of 108.5 nm. The ground state energy of an electron of this ion will be
(a) 3.4 eV
(b) 13.6 eV
(c) 54.4 eV
(d) 122.4 eV

Answer : C

Question. The first line of Balmer series has wavelength 6563 Å. What will be the wavelength of the first member of Lyman series
(a) 1215.4 Å
(b) 2500 Å
(c) 7500 Å
(d) 600 Å

Answer : A

Question. The energy of hydrogen atom in nth orbit is En then the energy in nth orbit of singly ionised helium atom will be
(a) 4En
(b) En/4
(c) 2En
(d) En/2

Answer : A

Question. The ionization energy of hydrogen atom is 13.6 eV.
Following Bohr’s theory, the energy corresponding to a transition between 3rd and 4th orbit is
(a) 3.40 eV
(b) 1.51 eV
(c) 0.85 eV
(d) 0.66 eV

Answer : D