The correct option for defining a molal (m) solution is Option A: 1000 g of solvent.

Molality is a measure of the concentration of a solution in terms of the amount of substance in a given mass of the solvent. It is defined as the number of moles of solute per kilogram of solvent. Thus, a 1 molal solution contains one mole of solute in 1000 grams (which is one kilogram) of the solvent. This measurement is independent of the temperature because it is based on mass rather than volume, which can fluctuate with temperature changes.

Option B (1.0 L of solvent) refers to a volumetric method of specifying concentration, but it is not how molality is defined. This might be more relevant to molarity, which is defined as moles of solute per liter of solution, not solvent.

Option C (1.0 L of solution) describes a unit related to the volume of the solution, not the mass of the solvent, and therefore does not describe molality.

Option D (22.4 L of solution) refers to a specific volume that is not related to the definition of molality. It may be mistaken with the molar volume of an ideal gas at standard temperature and pressure (STP), but it has no relation to molality.

Accordingly, the correct answer is Option A: 1000 g of solvent, which aligns with the definition of a molal solution as containing one mole of solute per kilogram (1000 g) of solvent.