A radioactive sample at any instant has its disintegration rate 5000 disintegrations per minute. After 5 minutes, the rate is 1250 disintegrations per minute. Then, the decay constant (per minute) is :

Question

( A ) 0.4 ln 2
( B ) 0.2 ln 2
( C ) 0.1 ln 2
( D ) 0.8 ln 2