Answer
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).
