Here's how to write the balanced net ionic equation for the reaction of magnesium with hydrochloric acid:

1. Write the complete balanced chemical equation:

Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g)

2. Write the complete ionic equation:

Mg(s) + 2H⁺(aq) + 2Cl⁻(aq) → Mg²⁺(aq) + 2Cl⁻(aq) + H₂(g)

3. Identify the spectator ions:

Spectator ions are ions that appear on both sides of the equation and do not participate in the reaction. In this case, the chloride ions (Cl⁻) are spectator ions.

4. Write the net ionic equation by removing the spectator ions:

Mg(s) + 2H⁺(aq) → Mg²⁺(aq) + H₂(g)

Therefore, the balanced net ionic equation for the reaction of magnesium with hydrochloric acid is:

Mg(s) + 2H⁺(aq) → Mg²⁺(aq) + H₂(g)