Answer
a. $V$ or $As$
b. Selenium
c. Vanadium
d. Krypton
Work Step by Step
a. In the $4^{th}$ period , $[Ar]4s^{2}3d^{3}$ or $[Ar]4s^{2}3d^{10}4p^{3}$ configurations will have 5 valence electrons. These are configurations of $V$ and $As$
b. In the $4^{th}$ period , $[Ar]4s^{2}3d^{10}4p^{4}$ configuration is of Selenium
c. In the $4^{th}$ period , $[Ar]4s^{2}3d^{3}$ configuration is of Vanadium
d. In the $4^{th}$ period , $[Ar]4s^{2}3d^{10}4p^{6}$ configuration is of a complete outer shell. This is of krypton.
