Which of the following describes absorbance in a UV-Vis spectrum?

Absorbance in a UV-Vis spectrum is defined as the measure of light absorbed by a substance. When light passes through a sample, some of that light is absorbed by the molecules in the sample, and absorbance quantifies this interaction. In UV-Vis spectroscopy, absorbance is directly proportional to the concentration of the absorbing species in the solution according to the Beer-Lambert law. This law states that absorbance is equal to the logarithm of the ratio of incident light intensity to transmitted light intensity. Thus, absorbance provides critical information about the identity and concentration of the substances in a solution, making it an essential parameter in analytical chemistry.

The other options describe different phenomena: light transmitted through a solution pertains to transmittance rather than absorbance, the speed of a reaction is related to kinetics rather than light measurements, and reflection involves light bouncing off surfaces rather than being absorbed, which is not relevant to the concept of absorbance in spectroscopy.