Half-life of radioactive substance is 60 min. During 3 hrs, the fraction of total no. of atom have decayed would be

Options

A. 0.125
B. 0.875
C. `8.5%`
D. 0.25

Answer

B

Explanation

Half life `(t_(1//2)) =1` hr Time for decay (T) = 3 hrs
`T = n xx t_(1//2)` So, `3 = n xx 1 or n =1 ` Let the original amount be `= N_(0)`
let the amount left after three half life periods be = N
Fraction ` = (N)/(N_(0)),` We know that , `N = [(1)/(2)]^(n)N_(0) " "(N)/(N_(0)) = ((1)/(2)^(n) = ((1)/(2))^(3) = (1)/(8)`
Thus, the fraction of total no. of atoms decayed ` = (7)/(8) = 87.5%`