Answer
The number of electrons in the highest occupied subshell for selenium is $4$
Work Step by Step
The element selenium $(Z=34)$ has $34$ electrons. In its part of the periodic table, the subshells of the electronic states are filled in the sequence
$1s\;2s\;2p\;3s\;3p\;3d\;4s\;4p....$
In the given sequence, the electronic configuration of selenium becomes
$1s^2\;2s^2\;2p^6\;3s^2\;3p^6\;3d^{10}\;4s^2\;4p^4$
Therefore, the highest occupied subshell for selenium is $4p$ and number of electrons in it is $4$.
