Two elements $X$ and $Y$ have atomic numbers $11$ and $16$ respectively.
$(a)$ Write the electronic configuration of both.
$(b)$ Which type of bond will they form?
$(c)$ Write the formula of the compound formed by their combination (in terms of $X$ and $Y$).

(C) Electronic configuration:

Element	$K$	$L$	$M$
$X_{11}$	$2$	$8$	$1$
$Y_{16}$	$2$	$8$	$6$

$(b)$ They will form an ionic bond.
Reason: $X$ has $1$ valence electron and will lose it to form $X^+$ ion. $Y$ has $6$ valence electrons and will gain $2$ electrons to form $Y^{2-}$ ion. The bond formed by the transfer of valence electrons from a metal $(X)$ to a non-metal $(Y)$ is called an ionic or electrovalent bond.
$(c)$ Formula of the compound:

Symbol	Valency
$X$	$+1$
$Y$	$-2$

By criss-cross method,the formula is $X_2Y$.