Answer
C and D are correct.
Work Step by Step
a) $Al^{3+}$ and $Cl^{-}$ would result in $AlCl_3$
b) $K^{+}$ and $F^{-}$ would result in $KF$
c) $Ga^{3+}$ and $O^{2-}$ results in $Ga_2O_3$
d) $Mg^{2+}$ and $S^{2-}$ results in $MgS$
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