NEET Physics Atom MCQs Set A

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) 18 pm
• b) 53 pm
• c) 27 pm
• d) 13 pm

Answer: 18 pm

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: of the electrons not being subject to a central force

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: because Bohr model gives in correct values of angular momentum

Question: O₂ 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: is not important because nuclear forces are short – ranged

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) 13.6 eV
• c) 20.40 eV
• d) 27.2 eV

Answer: 10.20 eV

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) 5/27
• b) 4/9
• c) 27/5
• d) 9/4

Answer: 5/27

Question:

Assertion : Between any two given energy levels, the number of absorption transitions is always less than the number of emission transitions.
Reason : Absorption transitions start from the lowest energy level only and may end at any higher energy level. But emission transitions may start from any higher energy level and end at any energy level below it.

• a) If both Assertion and Reason are correct and Reason is the correct explanation of Assertion
• b) If both Assertion and Reason are correct, but Reason is not the correct explanation of Assertion.
• c) If Assertion is correct but Reason is incorrect.
• d) If both the Assertion and Reason are incorrect

Answer: If both Assertion and Reason are correct and Reason is the correct explanation of Assertion

Question: 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 decreases, potential energy increases but total energy remains same
• c) kinetic energy, potential energy and total energy decrease
• d) kinetic energy and total energy decrease but potential energy increases

Answer:  its kinetic energy increases but potential energy and total energy decrease

Question: Given the value of Rydberg constant is 10⁷m^–1, the wave number of the last line of the Balmer series in hydrogen spectrum will be

• a) 0.25 × 10⁷ m^–1
• b) 0.025 × 10⁴ m^–1
• c) 0.5 × 10⁷ m^–1
• d) None of these

Answer: 0.25 × 10⁷ m^–1

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) 2
• b) 5
• c) 3
• d) 4

Answer: 2

Question: If the series limit wavelength of Lyman series for the hydrogen atom is 912 Å, then the series limit wavelength for Balmer series of hydrogen atoms is

• a) 912 × 4 Å
• b) 912 Å
• c) 912 × 2 Å
• d) None of these

Answer: 912 × 4 Å

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

• a) 4
• b) 0.5
• c) 2
• d) 1

Answer: 4