An element X has electronic configuration, $1s^{2}2s^{2}2p^{6}3s^2.$ What would be the expected formula of X with chloride.

According to the given electronic configuration, total number of electrons present in X is 12, and it corresponds to Mg. It's a metal, and its outermost orbit has two electrons. As it is a metal, it can donate its two electrons and obtain the closest noble gas structure.

Valence electronic configuration of Cl is 3s² 3p⁵. This depicts that Cl needs only one electron to complete its octet. As a result, one Mg combined with 2Cl and forms MgCl₂. As a result, element X with chloride has the formula XCl₂.