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)=0.693xx`mean life
`=0.693xx5=3.465` hours
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.