A volumetric flask calibrated at 20°C would contain more volume if the:

The correct answer is based on the principle of thermal expansion of liquids. When a liquid is heated, it expands and occupies a larger volume. If you have a volumetric flask that is calibrated to hold a specific volume at 20°C, heating the liquid before measurement will cause the liquid to expand and overflow, resulting in a greater volume than anticipated when the flask is at a lower temperature.

This is because most liquids, including common laboratory solvents such as water and ethanol, exhibit an increase in volume with an increase in temperature. Therefore, if the liquid is heated before it is added to the volumetric flask, it will fill the flask more fully than it would at a lower temperature, which is why this option is correct.

The other scenarios involve cooling or lowering the temperature, which would lead to a decrease in the volume of the liquid. For instance, if the laboratory temperature is 18°C, the liquid is refrigerated, or the flask itself is refrigerated, these conditions would result in a smaller volume occupied by the liquid according to its thermal properties at those lower temperatures. Thus, they do not contribute to increased volume in the calibration context.