3 should be isotope.
Emitting one alpha
Emitting 2 beta
I think in 5th Beta- is considered since it is more common.Still should be 6 and 8 both since they haven't mentioned it.
I remember seeing this in Neeraj Kumar and answer was C with reason as zero order.
To C kaise ?
Haan B. My bad. B is what was given in Neeraj Kumar