Half-life of a substance is `10` years. In what time, it becomes `(1)/(4) th` part of the initial amount ?

Options

A. 5 years
B. 10 years
C. 20 years
D. None of these

Answer

C

Explanation

( c) `N = N_0 e^(-t//T_(1//2)) rArr (1)/(4) = e^(-t//10)`
`rArr ((1)/(2))^2 =(1)/(e^(t//10)) rArr t = 20 years`.