A radioactive sample had an initial activily of 56 dpm (disintegration per min). After `69.3 min` it was found to have an activity of 28 dpm. Find the number of atoms in a sample having an activity of 10 dpm.

Options

A. 693
B. 1000
C. 100
D. 10000

Answer

B

Explanation

Initial activity = 56 dpm
after `69.3` min
activity = 28 dpm
`:. T_(1//2) =69.3 min " " lambda =(0.693)/(t_(1//2))=(0.693)/(69.3)=10^(-2min)`
Activity `=lambda N`
`10=10^(-2)xxN " " rArr " " N=1000`