Increasing the temperature generally affects the solubility of solutes in solvents. When the temperature of a solvent is increased, the solvent molecules gain kinetic energy, which results in more molecular motion. In the case of a solid solute, the increased motion of the solvent molecules causes the solvent to be able to dissolve more of the solute, thus increasing the solubility of the solid. Conversely, in the case of a gaseous solute, the increased motion of the solvent molecules causes the gas molecules to escape from the solution more easily, thus decreasing the solubility of the gas. Therefore, the correct option is: "increases the solubility of a solid in a liquid but decreases the solubility of a gas in a liquid."