A radioactive substance has an average life of `5` hours. In a time of `5` hours

Options

A. All active nuclei will decay
B. Less than 50% of the active nuclei will decay
C. Less than 60% of the active nuclei will decay
D. More than 70% of the active nuclei will decay

Answer

D

Explanation

Mean life (average life ) =`1/lamda " where " lamda` is the decay constant and half life `T = (0.693)/(lamda) = 0.693 xx "meanlife"`
`= 0.693xx 5 = 3.465` hour
Thus in 3.465 hour - 50% of the material will decay .
`therefore` In 5 hours - 72% of the material will decay.
Thus more than 70% of the active nuclei will decay.