NEET Physics Nuclei Questions Solved

A radioactive sample at any instant has its disintegration rate 5000 disintegration per minute. After 5 minutes, the rate is 1250 disintegrations per minute. Then, the decay constant (per minute) is 
(a) 0.8 In 2                (b) 0.4 In 2
(c) 0.2 In 2                (d) 0.1 In 2