An element belongs to the third period and second group of the periodic table:
$(a)$ State the number of valence electrons in it.
$(b)$ Is it a metal or a non-metal?
$(c)$ Name the element.
$(d)$ Write the formula of its oxide.

(N/A) The element belongs to group $2$,so it has $2$ valence electrons.
$(b)$ Elements in group $2$ are alkaline earth metals,so it is a metal.
$(c)$ The element in the third period and second group is Magnesium $(Mg)$.
$(d)$ Magnesium has a valency of $2$ and oxygen has a valency of $2$. The formula of its oxide is $MgO$.