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Atoms Class 12 MCQs Questions with Answers
Solving the Atoms Multiple Choice Questions of Class 12 Physics Chapter 12 MCQ can be of extreme help as you will be aware of all the concepts. These MCQ Questions on Atoms Class 12 with answers pave for a quick revision of the Chapter thereby helping you to enhance subject knowledge. Have a glance at the MCQ of Chapter 12 Physics Class 12 and cross-check your answers during preparation.
I. Choose the correct answer
Question 1.
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
Answer: (a) of the electrons not being subject to a central force.
Question 2.
A set of atoms in an excited state decay.
(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
Answer: (a) in general, to any of the states with lower energy.
Question 3.
The ground state energy of hydrogen atom is -13.6 eV. The kinetic and potential energies of the electron in this state are
(a) -13.6 eV, 27.2 eV
(b) 13.6 eV,-13.6 eV
(c) 13.6 eV,-27.2 eV
(d) 27.2 eV,-27.2 eV
Answer
Answer: (c) 13.6 eV,-27.2 eV
Question 4.
If the series limit frequency of the Lyman series is vL, then the series limit frequency of the Pfund series is:
(a) 16 vL
(b) vL/16
(c) VL/25
(d) 25 vL
Answer
Answer: (c) VL/25
Question 5.
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
Answer: (b) 1 : -1
Question 6.
Ionisation energy for hydrogen atom in the ground state is E. What is the ionisation energy of Li++ atom in the 2nd excited state
(a) E
(b) 3E
(c) 6E
(d) 9E
Answer
Answer: (a) E
Question 7.
Hydrogen (H\( _{ 1 }^{1}\)), deuterium (H\( _{ 1 }^{2}\)), singly ionised helium (He\( _{ 2 }^{4}\))+ and doubly ionised lithium (Li\( _{ 3 }^{6}\))++ all have one electron around their nucleus. Consider an electron transition from n = 2 to n = 1 if the wavelengths of the emitted radiations are λ1, λ2, λ3 and λ4 respectively then approximately which of the following is correct?
(a) 4λ1 = 2λ2 = 2λ3 = λ4
(b) λ1 = 2λ2 = 2λ3 = λ4
(c) λ1 = λ2 = 4λ3 = 9λ4
(d) λ1 = 2λ2 = 3λ3 = 4λ4
Answer
Answer: (c) λ1 = λ2 = 4λ3 = 9λ4
Question 8.
As an electron makes a transition from an excited state to the ground state of a hydrogen like atom/ion:
(a) its kinetic energy increases but potential energy and total energy decrease
(b) kinetic energy, potential energy and total energy decrease
(c) kinetic energy decreases, potential energy increases but total energy remains the same
(d) kinetic energy and total energy decrease but potential energy increases
Answer
Answer: (a) its kinetic energy increases but potential energy and total energy decrease
Question 9.
An electron from various excited states of hydrogen atom emits radiation to come to the ground state. Let λn, λg be the de-Broglie wavelength of the electron in the nth state and the ground state respectively. Let ∧n be the wavelength of the emitted photon in the transition from the nth state to the ground state. For large n (A, B are constants)
(a) ∧n = A + Bλn
(b) ∧n = A + Bλ\(_{ n }^{2}\)
(c) ∧\(_{ n }^{2}\) = X
(d) ∧n = A + \(\frac { B }{λ_n^2}\)
Answer
Answer: (d) ∧n = A + \(\frac { B }{λ_n^2}\)
II. Fill in the blanks
Question 1.
The a-scattering experiment was performed around 1911 by ……………… and ………………
Answer
Answer: Geiger, Marsden
Question 2.
One in ……………… α-particles retraced their path in the a scattering experiment.
Answer
Answer: 8000
Question 3.
The angle of scattering θ for zero value of impact parameter b is ………………
Answer
Answer: 180°
Question 4.
The scattering angle will decrease with the ……………… in impact parameter.
Answer
Answer: Increase
Question 5.
The smallest distance between the nucleus and the alpha particle for a head-on collision towards the nucleus is called the ………………
Answer
Answer: Distance of closest approach
Question 6.
The radius of an atom is about ……………… m and that of nucleus is ……………… m.
Answer
Answer: 10-10 and 10-15
Question 7.
The Rutherford’s model of an atom cannot explain the characteristics ……………… spectrum emitted by H-atom.
Answer
Answer: Line
Question 8.
When an electron jumps from an outer stationary orbit of energy E2 to an inner stationary orbit of energy E1 the frequency of radiation emitted = ………………
Answer
Answer: v = \(\frac { E_2 – E_1 }{h}\)
Question 9.
If the size of first orbit of hydrogen atom is 0.5 Å, the size of second orbit of hydrogen atom would be ………………
Answer
Answer: 2 Å
Question 10.
The frequency spectrum of radiation emitted as per Rutherford’s model of atom is ………………
Answer
Answer: Continuous
Question 11.
According to de Broglie a stationary orbit is that which contains an ……………… number of de-Broglie waves associated with the revolting electron.
Answer
Answer: integral
Question 12.
Energy possessed by an electron for (n → ∞)th orbit is ………………
Answer
Answer: Zero
Question 13.
The speed of an electron in the first orbit of hydrogen atoms is ………………
Answer
Answer: v = c/137n
Question 14.
The total energy of an electron in an orbit of hydrogen atom is ……………… of the kinetic energy.
Answer
Answer: Negative
Question 15.
The potential energy of the electron in an orbit of hydrogen atom is negative of ……………… the kinetic energy.
Answer
Answer: Twice
Question 16.
The ……………… energy is the energy required to excite an electron to a higher energy level.
Answer
Answer: Excitation
Question 17.
The ……………… energy is the energy required by an electron to set itself free.
Answer
Answer: Ionisation
Question 18.
Energy possessed by an electron in the ground state of hydrogen atom is ……………… eV.
Answer
Answer: -13.6
Question 19.
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
Answer: Negative
Question 20.
The value of Rydberg constant is ………………
Answer
Answer: 1.09 × 107 m-1
Question 21.
When an electron jumps from 2nd stationary orbit of hydrogen atom to 1st stationary orbit, the energy emitted is ………………
Answer
Answer: 10.2 eV
Question 22.
……………… series lies in the ultraviolet region.
Answer
Answer: Lyman
Question 23.
……………… of hydrogen spectrum which lies in the visible region electromagnetic spectrum.
Answer
Answer: Balmer series
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