Answer:
MgCl₂ + H₂ ---> 2 HCl + Mg
Step-by-step explanation:
Since you have not given any products, I am going to assume that this is a single-displacement reaction. In these types of reactions, an element is being swapped for another in a compound. The unbalanced equation would look like this:
MgCl₂ + H₂ ---> HCl + Mg
Mg does not have a subscript of 2 because it can exist by itself. As you can see, the reaction is not balanced. On the left side, there is 1 Mg, 2 Cl, and 3 H. On the right side, there is only 1 of each. The balanced equation would look like this:
MgCl₂ + H₂ ---> 2 HCl + Mg
Now, there is 1 Mg, 2 Cl, and 2 H on both sides.