The correct answer is: A. Temperature correction.
A hydrometer is an instrument used to measure the specific gravity or density of liquids. It works by floating in the liquid and measuring the depth to which it sinks. The depth of the hydrometer is then compared to a scale on the hydrometer to determine the specific gravity or density of the liquid.
The specific gravity or density of a liquid can change with temperature. This is because the molecules in a liquid move faster at higher temperatures, and this causes the liquid to expand. As the liquid expands, its density decreases.
To account for this change in density, hydrometer readings are corrected for temperature. This is done by using a table or chart that provides the correction factor for the specific gravity or density of the liquid at different temperatures.
The other options are incorrect because they are not factors that affect the accuracy of hydrometer readings. Meniscus correction is a correction that is made to account for the curvature of the surface of a liquid. Dispersing agent correction is a correction that is made to account for the presence of a dispersing agent in a liquid. Both of these corrections are relatively small and are not typically necessary for most applications.