Answer
a. aluminium
b. sulfur
c. argon
d. magnesium.
Work Step by Step
a. In the $3rd$ period , $[Ne]3s^{2}3p^{1}$ configurations will have 3 valence electrons. This is the configuration of aluminium
b. In the $3rd$ period , $[Ne]3s^{2}3p^{4}$ configuration is of sulfur
c. In the $3rd$ period , $[Ne]3s^{2}3p^{6}$ configuration is of argon
d. In the $3rd$ period , $[Ne]3s^{2}$ configuration is of magnesium.
