Final answer:
The equation Mg + HCl -> MgCl₂ + H₂ is balanced by changing the coefficient of HCl to 2, resulting in the balanced chemical equation: Mg + 2HCl → MgCl₂ + H₂. The correct answer is option A.
Step-by-step explanation:
The equation Mg + HCl -> MgCl₂ + H₂ can be balanced by changing the coefficient of HCl to 2. When we look at the reactants and products, we count the number of atoms for each element on both sides of the equation. Initially, we have 1 atom of Mg, 2 atoms of H, and 2 atoms of Cl in the reactants.
These must match with the products for the equation to be balanced. Changing the coefficient of HCl to 2 ensures there are the same number of atoms on both sides, making the final balanced equation: Mg + 2HCl → MgCl₂ + H₂.
It is not correct to change the coefficient of MgCl₂ to 0.5, change H₂ to H, change MgCl₂ to MgCl, or change the coefficient of Mg to 2 because these alterations would not balance the equation properly in terms of atoms of each element and in terms of charge.