CBSE Class 12 Physics Atoms MCQs Set E

Question: Consider an electron in the n^th orbit of a hydrogen atom in the Bohr model. The circumference of the orbit can be expressed in terms of de Broglie wavelength λ of that electron as
(a) (0.529)nλ
(b) √nλ
(c) (13.6)λ
(d) nλ
Answer: d

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

Question: The total energy of an electron in the first excited state of hydrogen atom is about –3.4 eV. Its kinetic energy in this state is
(a) 3.4 eV
(b) 6.8 eV
(c) –3.4 eV
(d) –6.8 eV
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: 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: Ratio of longest wavelengths corresponding to Lyman and Balmer series in hydrogen spectrum is
(a) 7/29
(b) 9/31
(c) 5/27
(d) 5/23
Answer: c

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: 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: An electron in the hydrogen atom jumps from excited state n to the ground state. The wavelength so emitted illuminates a photosensitive material having work function 2.75 eV. If the stopping potential of the photoelectron is 10 V, then the value of n is
(a) 2
(b) 3
(c) 4
(d) 5
Answer: c

Question: The electron in the hydrogen atom jumps from excited state (n = 3) to its ground state (n = 1) and the photons thus emitted irradiate a photosensitive material. If the work function of the material is 5.1 eV, the stopping potential is estimated to be (the energy of the electron in n^th state E_n = −13.6/n²,. eV )
(a) 5.1 V
(b) 12.1 V
(c) 17.2 V
(d) 7 V 
Answer: d

Question: In terms of Bohr radius a0, the radius of the second Bohr orbit of a hydrogen atom is given by
(a) 4a₀
(b) 8a₀
(c) √2a₀
(d) 2a₀
Answer: a

Question: When an electron does transition from n = 4 to n = 2, then emitted line spectrum will be
(a) first line of Lyman series
(b) second line of Balmer series
(c) first line of Paschen series
(d) second line of Paschen series.
Answer: b

Question: An electron makes a transition from orbit n = 4 to the orbit n = 2 of a hydrogen atom. What is the wavelength of the emitted radiations?
(R = Rydberg’s constant)
(a) 16/4R
(b) 16/5R
(c) 16/2R
(d) 16/3R 
Answer: d

Question: Consider 3^rd 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 interplanar distance in a crystal is 2.8 × 10^–8 m. The value of maximum wavelength which can be diffracted
(a) 2.8 × 10^–8 m
(b) 5.6 × 10^–8 m
(c) 1.4 × 10^–8 m
(d) 7.6 × 10^–8 m
Answer: b

Question: Hydrogen atoms are excited from ground state of the principle quantum number 4. Then the number of spectral lines observed will be
(a) 3
(b) 6
(c) 5
(d) 2
Answer: b

Question: An electron in hydrogen atom makes a transition n₁ → n₂ where n₁ and n₂ 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 n₁ and n₂ are
(a) n₁ = 6 and n₂ = 2
(b) n₁ = 8 and n₂ = 1
(c) n₁ = 8 and n₂ = 2
(d) n₁ = 4 and n₂ = 2
Answer: d

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 minimum wavelength of the X-rays produced by electrons accelerated through a potential difference of V volts is directly proportional to
(a) 1/√V
(b) 1/V
(c) √V
(d) V²
Answer: b

Question: Which source is associated with a line emission spectrum?
(a) Electric fire
(b) Neon street sign
(c) Red traffic light
(d) Sun
Answer: b

Question: 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) 3
(b) 4
(c) 1
(d) 2 
Answer: d

Question: 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) 6.8 eV
(b) 13.6 eV
(c) 1.7 eV
(d) 3.4 eV
Answer: d

Question: To explain his theory, Bohr used
(a) conservation of linear momentum
(b) quantisation of angular momentum
(c) conservation of quantum frequency
(d) none of these
Answer: b

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
Answer: a

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: An alpha nucleus of energy (1/2)mv² bombards a heavy nuclear target of charge Ze. Then the distance of closest approach for the alpha nucleus will be proportional to
(a) 1/Ze
(b) v²
(c) 1/m
(d) 1/v⁴
Answer: c

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 (μ–) [charge same as electron and mass 207 m_e], 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: In a Rutherford scattering experiment when a projectile of charge z₁ and mass M₁ approaches a target nucleus of charge z₂ and mass M₂, the distance of closest approach is r₀. The energy of the projectile is
(a) directly proportional to z₁z₂
(b) inversely proportional to z₁
(c) directly proportional to mass M₁
(d) directly proportional to M₁ × M₂
Answer: a

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: 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 energy of hydrogen atom in nth orbit is E_n then the energy in nth orbit of singly ionised helium atom will be
(a) 4E_n
(b) E_n/4
(c) 2E_n
(d) E_n/2 
Answer: a

Question: The ground state energy of hydrogen atom is –13.6 eV. When its electron is in the first excited state, its excitation energy is
(a) 10.2 eV
(b) 0
(c) 3.4 eV
(d) 6.8 eV
Answer: a

Question: For which one of the following, Bohr model is not valid?
(a) Hydrogen atom
(b) Singly ionised helium atom (He⁺)
(c) Deuteron atom
(d) Singly ionised neon atom (Ne⁺)
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 ionization energy of the electron in the hydrogen atom in its ground state is 13.6 eV. The atoms are excited to higher energy levels to emit radiations of 6 wavelengths. Maximum wavelength of emitted radiation corresponds to the transition between
(a) n = 3 to n = 1 states
(b) n = 2 to n = 1 states
(c) n = 4 to n = 3 states
(d) n = 3 to n = 2 states
Answer: c

Question: Out of the following which one is not a possible energy for a photon to be emitted by hydrogen atom according to Bohr’s atomic model?
(a) 0.65 eV
(b) 1.9 eV
(c) 11.1 eV
(d) 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: The life span of atomic hydrogen is
(a) fraction of one second
(b) one year
(c) one hour
(d) one day
Answer: a

Question: Given the value of Rydberg constant is 10⁷ 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: 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 λ₁ : λ₂ emitted in the two cases is
(a) 7/5
(b) 27/20
(c) 27/5
(d) 20/7
Answer: d

Question: Maximum frequency of emission is obtained for the transition
(a) n = 2 to n = 1
(b) n = 6 to n = 2
(c) n = 1 to n = 2
(d) n = 2 to n = 6
Answer: a

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. According to Bohr’s theory, the spectral lines emitted by hydrogen will be
(a) one
(b) two
(c) three
(d) four.
Answer: c

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 a hydrogen atom is raised from the ground state to an excited state,
(a) both K.E. and P.E. increase
(b) both K.E. and P.E. decrease
(c) the P.E. decreases and K.E. increases
(d) the P.E. increases and K.E. decreases.
Answer: d

Question: The ionisation energy of hydrogen atom is 13.6 eV, the ionisation energy of a singly ionised helium atom would be
(a) 13.6 eV
(b) 27.2 eV
(c) 6.8 eV
(d) 54.4 eV 
Answer: d

Question: 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 × 10¹⁵ Hz
(b) 5 × 10¹⁵ Hz
(c) 1.6 × 10¹⁵ Hz
(d) 2.5 × 10¹⁵ Hz
Answer: c