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

nacl or sodium chloride is an ionic compound. this is because an ionic compound pertains to a compound that consists of positively and negatively charged ions. in this case, na (sodium) has a tendency to lose one electron when it reacts with with other atoms, so the resulting sodium ion contains 11 protons and 10 electrons, thus making it positively charged (na+), when chlorine reacts, it usually gains one electron to form an ion called chloride, thus making it negatively charged ( since the ions are oppositely charged, they attract.