In the compound MgCl2, the subscript 2 indicates

The subscript 2 indicates number of Cl atoms

The molecular formula shows the number of atoms of a compound

whereas the empirical formula is the simplest comparison of the atoms making up the compound

MgCl₂ is an ionic compound composed of Mg and Cl atoms

Mg is in group 2 which has a +2 charge, while Cl is in the Halogen group which has a charge of -1

If the two are bonded, the 2 electrons released by Mg will be bound by 2 Cl atoms, each of which atoms of Cl need 1 more electron in order to obtain a stable electron configuration such as a noble gas

So the number 2 in the MgCl compound indicates the number of Cl atoms

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