$(i)$ Write the electronic configurations of the following ions:
$(a)$ $H^{-}$
$(b)$ $Na^{+}$
$(c)$ $O^{2-}$
$(d)$ $F^{-}$
$(ii)$ What are the atomic numbers of elements whose outermost electrons are represented by
$(a)$ $3s^{1}$
$(b)$ $2p^{3}$ and
$(c)$ $3p^{5}$?
$(iii)$ Which atoms are indicated by the following configurations?
$(a)$ $[He] 2s^{1}$
$(b)$ $[Ne] 3s^{2} 3p^{3}$
$(c)$ $[Ar] 4s^{2} 3d^{1}$

(N/A) $(i)$ $(a)$ $H^{-}$ ion: The electronic configuration of $H$ atom is $1s^{1}$. $A$ negative charge indicates the gain of an electron. $\therefore$ Electronic configuration of $H^{-} = 1s^{2}$.
$(b)$ $Na^{+}$ ion: The electronic configuration of $Na$ atom is $1s^{2} 2s^{2} 2p^{6} 3s^{1}$. $A$ positive charge indicates the loss of an electron. $\therefore$ Electronic configuration of $Na^{+} = 1s^{2} 2s^{2} 2p^{6}$.
$(c)$ $O^{2-}$ ion: The electronic configuration of $O$ atom is $1s^{2} 2s^{2} 2p^{4}$. $A$ dinegative charge indicates the gain of two electrons. $\therefore$ Electronic configuration of $O^{2-} = 1s^{2} 2s^{2} 2p^{6}$.
$(d)$ $F^{-}$ ion: The electronic configuration of $F$ atom is $1s^{2} 2s^{2} 2p^{5}$. $A$ negative charge indicates the gain of an electron. $\therefore$ Electronic configuration of $F^{-} = 1s^{2} 2s^{2} 2p^{6}$.
$(ii)$ $(a)$ $3s^{1}$: Configuration is $1s^{2} 2s^{2} 2p^{6} 3s^{1}$. Total electrons $= 11$. Atomic number $= 11$.
$(b)$ $2p^{3}$: Configuration is $1s^{2} 2s^{2} 2p^{3}$. Total electrons $= 7$. Atomic number $= 7$.
$(c)$ $3p^{5}$: Configuration is $1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{5}$. Total electrons $= 17$. Atomic number $= 17$.
$(iii)$ $(a)$ $[He] 2s^{1} = 1s^{2} 2s^{1}$. Atomic number $= 3$. Element is Lithium $(Li)$.
$(b)$ $[Ne] 3s^{2} 3p^{3} = 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{3}$. Atomic number $= 15$. Element is Phosphorus $(P)$.
$(c)$ $[Ar] 4s^{2} 3d^{1} = 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 4s^{2} 3d^{1}$. Atomic number $= 21$. Element is Scandium $(Sc)$.