Between 3 p.m. and 5 p.m. the average number of phone calls per minute coming into the helpline desk of a bank is 5. The probability that during one particular minute there will be only one phone call is :

$5e^{-5}$

The correct answer is Option (2) → $5e^{-5}$

The probability Mass function is,

$PMF(X=k)=\frac{e^{-λ}λ^k}{k!}$

$=\frac{e^{-5}5^{1}}{1!}=5e^{-5}$