Name two substances, equal masses of which interact with hydrochloric acid with the release of equal volumes of gas.

There are several solutions to this issue. This is possible due to the fact that the molar masses of both substances are the same. In this case, the gas does not have to be the same, because when calculating the volume of a gas using the formula, the amount of matter of this gas is important. Therefore, it must also be the same.
1) NaH and Mg: NaH + HCl => NaCl + H2 ↑; Mg + 2HCl => MgCl2 + H2 ↑;
2) KHCO3 and CaCO3: KHCO3 + HCl => KCl + H2O + CO2 ↑; CaCO3 + 2HCl => CaCl2 + H2O + CO2 ↑;
3) Ba and RbOCl: Ba + 2HCl => BaCl2 + H2 ↑; RbOCl + 2HCl => RbCl + H2O + Cl2 ↑