The number of f electrons in the ground state electronic...

$1{s}^{2}2{s}^{2}2{p}^{6}3{s}^{2}3{p}^{6}4{s}^{2}3{d}^{10}4{p}^{6}5{s}^{2}4{d}^{10}5{p}^{6}6{s}^{2} 4{f}^{14} 5{d}^{10}6{p}^{6}7{s}^{2} 5{f}^{4} 6{d}^{1}$

$Np 93 = \left[Rn 86\right]5{f}^{4}6{d}^{1}7{s}^{2}$

Total no. of electron in $f$ subshell $= 14$ in $4f$ and $4$ in $5f$ subshell $= 18{e}^{-}$