The half - life of `^(215) At` is `100 mu , s.`The time taken for the radioactivity of a sample of `^(215) At` to decay to `1//16^(th)` of its initially value is

Options

A. `400mus`
B. `6.3mus`
C. `40mus`
D. `300mus`

Answer

A

Explanation

If R is activity of radioactive substance after n half lives, then `R=R_(0)((1)/(2))^(n),(R_(0))/(16)=R_(0)((1)/(2))^(n)`
`therefore" "n=4, t=nT_(1//2)=4xx100=400mus`