In the given nuclear reaction A, B, C, D, E represents
${}_{92}{}^{238}\mathrm{U}\stackrel{\mathrm{\alpha }}{\to }{}_{\mathrm{B}}{}^{\mathrm{A}}\mathrm{Th}\stackrel{\mathrm{\beta }}{\to }{}_{\mathrm{D}}{}^{\mathrm{C}}\mathrm{Pa}\stackrel{\mathrm{E}}{\to }{}_{92}{}^{234}\mathrm{U}$

(1) A = 234, B = 90, C = 234, D = 91, E = $\mathrm{\beta }$

(2) A = 234, B = 90, C = 238, D = 94, E =$\mathrm{\alpha }$

(3) A = 238, B = 93, C = 234, D = 91, E = $\mathrm{\beta }$

(4) A = 234, B = 90, C = 234, D = 93, E = $\mathrm{\alpha }$

If half life of a radioactive element is 3 hours, after 9 hours its activity becomes 

(1) 1/9                     

(2) 1/27

(3) 1/6                     

(4) 1/8

At any instant the ratio of the amount of radioactive substances is 2 : 1. If their half lives be respectively 12 and 16 hours, then after two days, what will be the ratio of the substances?

(1) 1 : 1                 

(2) 2 : 1

(3) 1 : 2                 

(4) 1 : 4

Which of the following isotopes is used for the treatment of cancer 

(1) ${\mathrm{K}}^{40}$        

(2) ${\mathrm{Co}}^{60}$

(3) ${\mathrm{Sr}}^{90}$       

(4) ${\mathrm{I}}^{131}$

If half-life of a radioactive atom is 2.3 days, then its decay constant would be 

(1) 0.1           

(2) 0.2

(3) 0.3           

(4) 2.3

A radio isotope has a half life of 75 years. The fraction of the atoms of this material that would decay in 150 years will be

(1) 66.6%               

(2) 85.5%

(3) 62.5%               

(4) 75%

An artificial radioactive decay series begins with unstable ${}_{94}{}^{241}\mathrm{Pu}$. The stable nuclide obtained after eight α decays and five $\mathrm{\beta }$-decays is 

(1) ${}_{83}{}^{209}\mathrm{Bi}$         

(2) ${}_{82}{}^{209}\mathrm{Pb}$

(3) ${}_{82}{}^{205}\mathrm{Ti}$         

(4) ${}_{82}{}^{201}\mathrm{Hg}$

The activity of a sample is $64\times {10}^{-5}$ Ci. Its half-life is 3 days. The activity will become $5\times {10}^{-6}$ Ci after 

(1) 12 days         

(2) 7 days

(3) 18 days         

(4) 21 days

The half-life of radon is 3.8 days. Three forth of a radon sample decay in

(1) 5.02 days         

(2) 15.2 days

(3) 7.6 days           

(4) 11.4 days

A nucleus of an element ${}_{84}{}^{202}\mathrm{X}$ emits an $\mathrm{\alpha }$-particle first, a $\mathrm{\beta }$-particle next and then a gamma photon. The final nucleus formed has an atomic number 

(1) 200           

(2) 199

(3) 83             

(4) 198