Lattice energy of an ionic compound depends upon

The electronic configurations of four elements $L$,$P$,$Q$,and $R$ are given in the brackets:
$L(1s^2, 2s^2 2p^4); Q(1s^2, 2s^2 2p^6, 3s^2 3p^5)$
$P(1s^2, 2s^2 2p^6, 3s^1); R(1s^2, 2s^2 2p^6, 3s^2)$
The formulae of ionic compounds that can be formed between these elements are:

Ionic compounds are formed most easily with

The pair in which the first compound is ionic and the second compound is covalent,is

For ionic solids,choose the correct option using $T$ (True) or $F$ (False) for the following statements:
$(1)$ They have very high melting and boiling points.
$(2)$ They are electrolytes.
$(3)$ They possess directional bond characteristics.
$(4)$ They can have isomorphic types of structures.

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