If `N_(0)` is the initial mass of a substance with half-life `t_(1//2) = 5` years, then the amount of substance left after 15 years is

Options

A. `(N_(0))/(8)`
B. `(N_(0))/(16)`
C. `(N_(0))/(2)`
D. `(N_(0))/(4)`

Answer

A

Explanation

`N/N_(0)=(1/2)^(n)` where n are is number of half-lives. If `T_(1//2)=5` years then in `15` years, `n=3`
`implies N/N_(0)=(1/2)^(3)=1/8 implies N=N_(0)/8`