Given below are two statements.
Assertion (A):
For a random variable \(X\), if \(x=0,1,2,\ldots\) and
\[
P(X=x)=k\frac{\lambda^x}{x!},
\]
then for it to be a probability mass function, \(k=e^{-\lambda}\).
Reason (R):
In a probability distribution, the sum of all probabilities must be \(1\).