Which equation represents the volume of gas in dm³?

The correct equation for representing the volume of gas in cubic decimeters (dm³) relates to the concept of molar volume at standard temperature and pressure (STP). Specifically, under these conditions, one mole of gas occupies approximately 24 dm³.

In the correct equation, the mass of the gas in grams is divided by its molar mass (Mr), which gives the number of moles of gas present. By multiplying this value by 24, you convert the amount of substance (in moles) into volume (in dm³). Therefore, this equation accurately describes how to calculate the volume of a gas based on its mass and molar mass, making it a useful tool in stoichiometry and gas laws.

Other choices provide incorrect methods for calculating the volume of gas. One option suggests multiplying the mass by the molar mass, which doesn't relate directly to volume. Another option involves using 22 dm³, which applies to a different set of conditions (like one mole of an ideal gas at room temperature and pressure, not STP), and one option incorrectly sums mass and molar mass, which does not correspond to any accurate physical interpretation regarding gas volume.