`90%` of the active nuclei present in a radioactive sample are found to remain undecyayed after `1` day. The precentage of undecayed nuclei left after two days will be

Options

A. `85%`
B. `81%`
C. `80%`
D. `79%`

Answer

B

Explanation

`N = N_(0)e^(-lambdat)`
`0.90N_(0) = N_(0)e^(-lambdaxx1) rArr e^(-lambda) = 0.9`
`N_(1) = N_(0)e^(-lambdat) = N_(0)e^(-lambdaxx2) =N_(0)e^(-2lambda)= N_(0)(e^(-lambda)) = 0.81 N_(0)`
`(N_(1))/(N_(0)) =0.81` i.e. `81%`
OR
The rule of half-life is applicable for any fraction of life.
`N_(0)overset(1day)rarr(9)/(10)N_(0) overset(1day)rarr((9)/(100))^(2)N_(0)`.