Write the electronic configuration of the following ions:
$(a) H^-$
$(b) Na^+$
$(c) O^{2-}$
$(d) F^-$

$(a) H^-$: Total electrons = $1 + 1 = 2$. Electronic configuration: $1s^2$.
$(b) Na^+$: Total electrons = $11 - 1 = 10$. Electronic configuration: $1s^2 2s^2 2p^6$.
$(c) O^{2-}$: Total electrons = $8 + 2 = 10$. Electronic configuration: $1s^2 2s^2 2p^6$.
$(d) F^-$: Total electrons = $9 + 1 = 10$. Electronic configuration: $1s^2 2s^2 2p^6$.