The formula of manesium chloride (or magnesium chlorine) is:
[tex] \bf~MgCl_{2} [/tex]
In the formula, the number "2" represents the number of chlotine atoms that are bonded with one magensium atom.
In this case, there are 2 chlorine atoms for every magensium atom as shown in the image below.
Hope it helped,
BioTeacher101