A radioactive element emits 200 particles per second. After three hours 25 particles per second are emitted. The half life period of element will be
(1) 50 minutes           

(2) 60 minutes

(3) 70 minutes           

(4) 80 minutes

The half life of the isotope ${}_{11}{}^{24}\mathrm{Na}$ is 15 hrs. How much time does it take for $\frac{7}{8}\mathrm{th}$ of a sample of this isotope to decay

(1) 75 hrs               

(2) 65 hrs

(3) 55 hrs               

(4) 45 hrs

If the half life of a radioactive sample is 10 hours,
its mean life is 

(1) 14.4 hours               

(2) 7.2 hours

(3) 20 hours                 

(4) 6.93 hours

If 20 gm of a radioactive substance due to radioactive decay reduces to 10 gm in 4 minutes, then in what time 80 gm of the same substance will reduce to 10 gm 

(1) In 8 minutes             

(2) In 12 minutes

(3) In 16 minutes             

(4) In 20 minutes

16 gm sample of a radioactive element is taken from Bombay to Delhi in 2 hour and it was found that 1 gm of the element remained (undisintegrated). Half life of the element is 

(1) 2 hour         

(2) 1 hour

(3) $\frac{1}{2}$ hour         

(4) $\frac{1}{4}\mathrm{hour}$

Unit of radioactivity is Rutherford. Its value is

(1) $3.7\times {10}^{10}$ disintegrations/sec

(2) $3.7\times {10}^6$ disintegrations/sec

(3) $1.0\times {10}^{10}$disintegrations/sec

(4) $1.0\times {10}^6$ disintegrations/sec

A radioactive substance has a half life of 60 minutes. After 3 hours, the fraction of atom that have decayed would be

(1) 12.5%               

(2) 87.5%

(3) 8.5%                 

(4) 25.1%

An element used for radioactive carbon dating for more than 5600 years is 

(1) C-14         

(2) U-234

(3) U-238       

(4) Po-94

N atoms of a radioactive element emit n alpha particles per second. The half life of the element is

(1) $\frac{\mathrm{n}}{\mathrm{N}}$ sec                   

(2) $\frac{\mathrm{N}}{\mathrm{n}}$ sec

(3) $\frac{0.693 \mathrm{N}}{\mathrm{n}}$ sec           

(4)  $\frac{0.693 \mathrm{n}}{\mathrm{N}}$ sec

The radioactive nucleus ${}_7{}^{13}\mathrm{N}$ decays to ${}_6{}^{13}\mathrm{C}$ through the emission of 

(1) Neutron             

(2) Proton

(3) Electron             

(4) Positron