Reaction between which of the following two reactants will produce hydrogen gas?

Q. Reaction between which of the following two reactants will produce hydrogen gas?

1. Magnesium and hydrochloric acid
2. Copper and dilute nitric acid
3. Calcium carbonate and hydrochloric acid
4. Zinc and nitric acid

Answer: Magnesium and hydrochloric acid

Magnesium reacts with hydrochloric acid according to the equation:

Mg(s) + 2 HCl(aq) --> MgCl ₂(aq) + H₂(g)

This demonstration can be used to illustrate the characteristic reaction of metals with acid, a single replacement reaction, or to demonstrate the generation of hydrogen gas.