Which is the correct equation for the reaction of magnesium with hydrochloric acid to produce hydrogen and magnesium chloride?

a. mg + 2 hcl → h2 + mgcl2

b. mg + hcl → h + mgcl

c. 2 mg + 6 hcl → 3 h2 + 2 mgcl2

d. mg + 2 hcl → 2 h + mgcl2

e. mg + 3 hcl → 3 h + mgcl2?

Answer is: a. Mg + 2HCl → H₂ + MgCl₂.

Reduction hald reaction: 2H⁺ + 2e⁻→ H₂.

Oxidation half reaction: Mg ⁰ → Mg²⁺ + 2e⁻.

In this chemical reaction, magnesium lost two electrons (oxidation, change oxidation number from 0 to + 2) and hydrogen gain that two electrons (reduction, change oxidation number from + 1 to 0).