The correct answer is (a)
Work Step by Step
The four quantum numbers are : $n$ = 4 (principal quantum number) $l$ = 1 for the p orbital $m_l$ has values from $-l$ to $+l$, so it can be 0. $m_s$ can be $+1/2$ or $-1/2$. All of these criteria are satisfied in option (a).