The half life period of a radioactive substance is 140 days. After how much time, 15 g will decay from a 16 g sample of the substance?

Options

A. 140 days
B. 560 days
C. 280 days
D. 420 days

Answer

B

Explanation

`(0.693)/(140) = (2.303)/(t) log (16)/(16-15) `= 560 days
or `[1/2]^4 = [1/2]^(t//140) implies 4 = t/(140) implies t = 560` days