What does spectrophotometry measure?

Spectrophotometry is a technique that measures how much light is absorbed by a substance at various wavelengths of electromagnetic radiation. This process involves passing a beam of light through a sample and detecting the intensity of light that emerges. The differences in intensity provide valuable information about the concentration and characteristics of the substance being analyzed, as different compounds absorb light at different wavelengths.

By focusing on the absorption of electromagnetic radiation, scientists can determine the presence and concentration of substances in a solution. This method is pivotal in many fields, including chemistry, biochemistry, and environmental science, where quantifying substances accurately is essential.

The other options refer to different types of measurements. Mass relates to weight, which cannot be determined through spectrophotometry. Electrical conductivity measures how well a solution can conduct electricity, focusing on ionic strength rather than light absorption. Density is a measure of mass per unit volume and does not pertain to light absorption at any wavelength. Therefore, the correct choice directly correlates to the fundamental principles of spectrophotometry.