Mg(s) + HCl (aq) ----> ?
In answering this kind of reaction, first we have to identify which among the elements have the tendency to form another compound.
-->Mg and Cl can form another compound which is MgCl2
-->H now will be released as gas in the form of H2.
Now, we can write the whole chemical equation as:
Mg (s) + HCl (aq) ----> MgCl2(aq) + H2 (gas)
Next, we have to ensure that the equation is balanced.
To do that, we have to check if both sides of the equation has equal
number of atoms.
--> There are twice the number of H and Cl present in the right side of the chemical equation. So we have to double the number of HCl on the left side to make the equation balanced.
Finally, we can rewrite the the balanced chemical equation as:
Mg (s) + 2HCl (aq) ----> MgCl2(aq) + H2 (gas)