80% of the radioactive nuclei present in a sample is found to remain undecayed after one day. The percentage of undecayed nuclei left after two days will be

Options

A. 64
B. 20
C. 46
D. 80

Answer

a

Explanation

`lambda = (2.303)/(t) log ((N_(0))/(N))`
`= (2.303)/(1) log ((100)/(80))`
`lambda = (2.303)/(2) log ((100)/(N))`
`(2.303)/(1) log ((100)/(80)) = (2.303)/(2) log ((100)/(N))`
`((5)/(4))^(2) = (100)/(N)`
`N = 64`