Fission of nuclei is possible because the binding energy per nucleon in them:

1.	increases with mass number at high mass numbers.
2.	decreases with mass number at high mass numbers.
3.	increases with mass number at low mass numbers.
4.	decreases with mass number at low mass numbers.

 Radioactive substance do not emit

(1) Electron           

(2) Helium nucleus

(3) Positron         

(4) Proton

During a negative beta decay 

Some radioactive nucleus may emit

(1) Only one $\mathrm{\alpha },\mathrm{\beta }$ or $\mathrm{\gamma }$ at a time

(2) All the three $\mathrm{\alpha },\mathrm{\beta }$ and $\mathrm{\gamma }$ one after another

(3) All the three $\mathrm{\alpha },\mathrm{\beta }$ and $\mathrm{\gamma }$ simultaneously

(4) Only $\mathrm{\alpha }$ and $\mathrm{\beta }$ simultaneously

Which can pass through 20 cm thickness of the steel

(1) $\mathrm{\alpha }$ particles                   

(2) $\mathrm{\beta }$ particles

(3) $\mathrm{\gamma }$ rays                         

(4) Ultraviolet rays

The half-life period of radium is 1600 years. Its average life time will be 
(a) 3200 years              (b) 4800 years
(c) 2319 years               (d) 4217 years

What percentage of original radioactive atoms is left after five half lives 

(1) 0.3%               

(2) 1%

(3) 31%                 

(4) 3.125%

Beta rays emitted by a radioactive material are

(1) Electromagnetic radiation

(2) The electrons orbiting around the nucleus

(3) Charged particles emitted by nucleus

(4) Neutral particles

Alpha rays emitted from a radioactive substance are

(1) Negatively charged particles

(2) Ionised hydrogen nuclei

(3) Doubly ionised helium atom

(4) Uncharged particles having the mass equal to proton

Half life of ${\mathrm{Bi}}^{210}$ is 5 days. If we start with 50,000
atoms of this isotope, the number of atoms left over after 10
days is 

(1) 5,000               

(2) 25,000

(3) 12,500             

(4) 20,000