An element z has an electronic configuration : ns2np6(n−1)d10(n−2)f14. Which value of n is not possible

For n=6,

$6 s^{2}, 6 p^{6}, 5 d^{10}, 4 f^{' 4}$

This is a possible electronic configuration.

For n=3,

$\begin{array}{l} \Rightarrow 3 s^{2}, 3 p^{6}, (3 - 1) d^{10} (3 - 2) f^{14} \\ \Rightarrow 3 s^{2}, 3 p^{6}, 2 d^{10}, 1 f^{14} \end{array}$

This is not possible.

For n=5,

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

This is not possible.

An element z has an electronic configuration : $n s^{2} n p^{6}$ $(n - 1) d^{10} (n - 2) f^{14}$ . Which value of n is not possible