question_answer

If \[{{N}_{0}}\] is the original mass of the substance of half-life period \[{{t}_{1/2}}=5\] yr, then the amount of substance left after 15 yr is         [AIEEE 2002]

A) \[\frac{{{N}_{0}}}{8}\]

B) \[\frac{{{N}_{0}}}{16}\]

C) \[\frac{{{N}_{0}}}{2}\]

D) \[\frac{{{N}_{0}}}{4}\]

Correct Answer: A

Solution :

[a]  is the initial amount of substance and N is the amount left after decay.

Thus,

number of half-lives

Therefore,