If half-life of a substance is `3.8` days and its quantity is `10.38 gm`. Then substance quantity remaining left after `19` days will be

Options

A. `0.151 gm`
B. `0.32 gm`
C. `1.51 gm`
D. `0.16 gm`

Answer

B

Explanation

(b) Number of half-lives `n = (19)/(3.8) = 5`, Now `(N)/(N_0) = ((1)/(2))^n`
`rArr (N)/(10.38) = ((1)/(2))^5 rArr N = 10.38 xx ((1)/(2))^5 = 0.32 gm`.