81.

Assertion:  Static crashes are heard on radio, when lightning flash occurs in the sky. 

Reason:  Electromagnetic waves having frequency of radio wave range interfere with radio waves.

• If both assertion and reason are true and reason is the correct explanation of assertion.

• If both assertion and reason are true but reason is not the correct explanation of assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.

Assertion:  γ-radiation emission occurs after $\mathrm{\alpha } \mathrm{and} \mathrm{\beta }$ decay. 

Reason: Energy levels occur in nucleus.

• If both assertion and reason are true and reason is the correct explanation of assertion.

• If both assertion and reason are true but reason is not the correct explanation of assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.

In nuclear fission, which of the following quantity is conserved?

• Energy

• Mass

• Momentum

• Both energy and mass

When a slow neutron is captured by a ${}_{92}{}^{235}\mathrm{U}$ nucleus, a fission energy releasing 200 MeV. If power of nuclear reactor is 100 W then rate of nuclear fission is

• 3.6 × 10⁶ s^-1

• 3.1 × 10¹² s^-1

• 1.8 × 10⁴ s^-1

• 4.1 × 10⁶ s^-1

Which of the following statement is incorrect?

• Neutron is less stable than proton

• Neutron can cause fission in nuclear reactors but proton can not.

• A free proton can emit beta particle.

• A bound proton can emit beta particle.

Electric field at a distance r from infinitely long conducting sheet is proportional to

• r^-1

• r^-2

• r^-3/2

• independent of r

In beta plus decay

• antineutrino is produced with electron

• neutrino is produced with positron

• neutron is produced with electron

• none of these

Assertion:  ${}_{27}{}^{60}\mathrm{Co}$  is a source of gamma radiation.

Reason: Gamma emission is due to nuclear decay.

• If both assertion and reason are true and reason is the correct explanation of assertion.

• If both assertion and reason are true but reason is not the correct explanation of assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.

Half life of a radio-active element is 8 years, how much amount will be present after 32 years?

• $\frac{1}{4}$

• $\frac{1}{8}$

• $\frac{1}{16}$

• $\frac{1}{32}$

Gamma decay takes place

• Prior to alpha decay.

• Prior to beta decay.

• Prior to positron decay.

• Due to de-excitment of nuclear levels.