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

The radioactive decay of uranium into thorium is expressed by the equation ${}_{92}{}^{238}\mathrm{U}\to {}_{90}{}^{234}\mathrm{Th}+\mathrm{X}$ where 'X' is

(1) An electron               

(2) A proton

(3) A deuteron                 

(4) An alpha particle

In a radioactive decay, neither the atomic number nor the mass number changes. Which of the following would be emitted in the decay process 

(1) Proton             

(2) Neutron

(3) Electron           

(4) Photon

The half life period of a radioactive substance is 5 min. The amount of substance decayed in 20 min will be

(1) 93.75%                 

(2) 75%

(3) 25%                       

(4) 6.25%