Class 12 Nuclei CBSE Questions & Answers

Class 12 · Nuclei

This is Physics Class 12 Nuclei CBSE Questions & Answers. There are 15 questions in this test with each question having around four answer choices.

Questions & Answers

1
Cadmium rods are used in a nuclear reactor for
  • A
    speeding up slow neutrons
  • B
    absorbing neutrons
  • C
    regulating the power level of the reactor.
    Correct
  • D
    slowing down fast neutrons
2
Choose the WRONG statement. A thermonuclear fusion reactor is better than a fission reactor for the following reason:
  • A
    A fusion reaction can be much more easily controlled than a fission
  • B
    For the same mass of substances involved, a fusion reaction releases much more energy than a fission reaction.
  • C
    A fusion reaction produces almost no radioactive waste.
  • D
    The fuel required for fusion is readily available in abundance from seawater.
    Correct
3
Which of the following particles can be added to the nucleus of an atom without changing its chemical properties?
  • A
    Electrons
  • B
    Protons
  • C
    Neutrons
    Correct
  • D
    Alpha Particles
4
The average number of neutrons released by the fission of one uranium atom is
  • A
    2.5
  • B
    2
  • C
    3.0
    Correct
  • D
    1
5
What is the main source of energy of the sun?
  • A
    Nuclear fission of heavier unstable elements in the sun
  • B
    Combustion of pure carbon present in the sun
  • C
    Gravitational energy liberated during the slow contraction of the sun.
  • D
    Nuclear fusion of lighter elements in the sun.
    Correct
6
What is the rest mass energy of an electron?
  • A
    1 eV
  • B
    0.51 MeV
    Correct
  • C
    931 MeV
  • D
    none of these
7
The chemical behavior of an atom depends upon
  • A
    the number of electrons orbiting around its nucleus
    Correct
  • B
    the number of nucleons in its nucleus.
  • C
    the number of protons in its nucleus
  • D
    the number of neutrons in its nucleus
8
After two hours 1/16th of the initial amount of a certain radioactive isotope remains undecayed. The half life of the isotope is
  • A
    15 min
  • B
    30 min
    Correct
  • C
    1 hour
  • D
    45 min
9
A radioactive element X has atomic number Z and atomic mass number A. It decays by the emission of an alpha particle and a gamma ray. The new element is
  • A
    \({}_{Z + 2}^{A + 4}Y\)
  • B
    \({}_Z^{A + 1}Y\)
  • C
    \({}_{Z - 2}^{A - 4}Y\)
  • D
    \({}_{Z - 2}^{A - 2}Y\)
    Correct
10
The radioactive decay of uranium into thorium is represented by the equation \({}_{92}^{238}U \to {}_{90}^{234}Th + x\) What is x?
  • A
    an electron
  • B
    proton
  • C
    an alpha particle
    Correct
  • D
    a neutron
11
The half life of a radioactive substance is 10 days. This means that
  • A
    the substance completely disintegrates in 40 days
  • B
    1/8 part of the mass of the substance will be left intact at the end of 40
  • C
    7/8 part of the mass of the substance disintegrates in 30 days
    Correct
  • D
    the substance completely disintegrates in 20 days
12
The half-life of a radioactive substance depends upon
  • A
    its temperature
  • B
    the strength of the nuclear force between the nucleons of its atoms
    Correct
  • C
    the mass of the substance
  • D
    the external pressure on it
13
Two radioactive sources A and B initially contain equal number of radioactive atoms. Source A has a half-life of 1 hour and source B has a half-life of 2 hours. At the end of 2 hours, the ratio of the rate of disintegration of A to that of B is
  • A
    1 : 4
  • B
    0.0423611111111
    Correct
  • C
    2 : 1
  • D
    1 : 2
14
A uranium nucleus (atomic number 92, mass number emits an alpha particle and the resultant nucleus emits a \(\beta \) particle. The atomic and mass numbers respectively of the final nucleus are
  • A
    90,236
  • B
    92,232
  • C
    91,234 Hz
    Correct
  • D
    90,240
15
When a nucleus emits a photon, what happens to its atomic number and its actual mass?
  • A
    Its atomic number and its actual mass both increase
  • B
    Its atomic number and its actual mass remain unchanged
  • C
    Its atomic number and its actual mass both decrease
  • D
    Its atomic number remains the same but its actual mass decreases
    Correct