The half life of radioactive substance is 10 year. How long will it take to reduce to one fourth of its original amount and what is the value of its decay constant ?

Options

A. 40 year , `(0.693)/(3)` / year
B. 30 year , `(0.693)/(2)` / year
C. 20 year, 0.0693 / year
D. 10 year, 0.00693 / year

Answer

C

Explanation

T = 10 years , after 10 years it will be reduced to half and after 20 years , it will be reduced to `1/4` of its original amount and
`because T = (0.693)/(lamda)`
`therefore lamda = (0.693)/(T) = (0.693)/(10) = 0.0693`