Assertion:When a nucleus is in an excited state, it can make a transition to a lower energy state by the emission of gamma rays .
Reason:These are energy levels for a nucleus just like there are energy levels in atoms .
A. If both assertion and reason are true and reason is the correct explanation of assertion .
B. If both assertion and reason are true but reason is not the correct explanation of assertion .
C. If assertion is true but reason is false .
D. If both assertion and reason are false
