Answer
The Lewis symbols are shown in the attached image
Work Step by Step
a) NaF is made of $Na^+$ and $F^-$.
b) CaO is made of $Ca^{2+}$ and $O^{2-}$.
c) $SrBr_2$ is made of $Sr^{2+}$ and 2 $Br^-$.
d) $K_2O$ is made of 2 $K^{+}$ and $O^{2-}$.
The cations have no valence electrons, and the anions have full octets.
