The process by which a heavy nucleus splits into light nuclei is known as 

(1) Fission           

(2) $\mathrm{\alpha }$-decay

(3) Fusion             

(4) Chain reaction

The explosion of the atomic bomb takes place due to

1. Nuclear fission           

2. Nuclear fusion

3. Scattering               

4. Thermionic emission

Energy generation in stars is mainly due to

(1) Chemical reactions               

(2) Fission of heavy nuclei

(3) Fusion of light nuclei             

(4) Fusion of heavy nuclei

Fusion reaction is initiated with the help of 

(1) Low temperature         

(2) High temperature

(3) Neutrons                     

(4) Any particle

When a ${}_4{}^9\mathrm{Be}$ atom is bombarded with $\mathrm{\alpha }$ particles, one of the product of nuclear transmutation is ${}_6{}^{12}\mathrm{C}$. The other is 

(1) ${}_{-1}{}^0\mathrm{e}$           

(2) ${}_1{}^1\mathrm{H}$

(3) ${}_1{}^2\mathrm{D}$            

(4) ${}_0{}^1\mathrm{n}$

During the nuclear fusion reaction 

(1) A heavy nucleus breaks into two fragments by itself

(2) A light nucleus bombarded by thermal neutrons breaks up

(3) A heavy nucleus bombarded by thermal neutrons breaks up

(4) Two light nuclei combine to give a heavier nucleus and  possibly other products

A gamma ray photon creates an electron- positron pair. If the rest mass energy of an electron is 0.5 MeV and the total K.E. of the electron- positron pair is 0.78 MeV, then the energy of the gamma ray photon must be 

(1) 0.78 MeV                 

(2) 1.78 MeV

(3) 1.28 MeV                 

(4) 0.28 MeV

Which of the following statement is true 

(1) ${}_{78}\mathrm{Pt}_{192}$ has 78 neutrons

(2) ${}_{84}\mathrm{Po}_{214}\to {}_{82}\mathrm{Pb}_{210}+{\mathrm{\beta }}^{-}$

(3) ${}_{92}U_{238}\to {}_{90}\mathrm{Th}_{234}+{}_2\mathrm{He}_4$

(4) ${}_{90}\mathrm{Th}_{234}\to {}_{91}\mathrm{Pa}_{234}+{}_2\mathrm{He}_4$

Fast neutrons can easily be slowed down by 

(1) The use of lead shielding

(2) Passing them through heavy water

(3) Elastic collisions with heavy nuclei

(4) Applying a strong electric field