The electronic configuration of 2 elements X and Y are

$X=1s^{2}2s^{2}2p^5$     $Y:1s^{2}2s^{2}2p^{6}3s^1$

The formula and nature of compound formed between X and Y

Y is monovalent metal

$Y\to Y^{+}+e$             $X+e^{-}\to X^{-}$

In between Y and X the bond is formed due to transfer of electron. Hence it is ionic in nature.

$Y^{+}+X^{-}\to YX$ .