If m represents an element in group 2 the formula of its chloride would be

MCl₂

Explanation:

Elements in Group 2 of the periodic table are alkaline earth metals and they have 2 electrons in their valence shell. To follow the octet rule, they tend to lose 2 electrons, forming cations M²⁺. Chloride is an anion of formula Cl⁻. For a compound to be electrically neutral, it requires 1 atom of M²⁺ and 2 atoms of Cl⁻ so that the total charge is zero: +2 + 2.(-1) = 0. The resulting formula is MCl₂