Question

After a certain lapse of time, fraction of radioactive polonium undecayed is found to be `12.5%` of the initial quantity. What is the duration of this time lapsed if the half life of polonium is 138 days ?
A. `414` days
B. `407` days
C. `421` days
D. `410` days

Answer 1

Correct Answer - A
`(dN)/(dt)=lambda N`, here `N="avagadrono"//238, lambda=0.693//T_((1)/(2))`