Which of the following has the highest melting point?

Which of the following is not correct regarding the properties of ionic compounds?

Select the incorrect statement.

An atom of an element $A$ has three electrons in its outermost shell and that of $B$ has six electrons in the outermost shell. The formula of the compound between these two will be

Use Lewis symbols to show electron transfer between the following atoms to form cations and anions:
$(a)$ $K$ and $S$
$(b)$ $Ca$ and $O$
$(c)$ $Al$ and $N$

The compound in which the cation is isoelectronic with the anion is