Concept:A photometer is an optical instrument used to measure the intensity or brightness of light.
Explanation:A photometer determines how much light energy falls on a surface or is emitted by a source per unit time.
It is commonly used to compare the brightness of different light sources and to check illumination levels.
For example, photographers use photometers to set correct exposure, and astronomers use them to measure the brightness of stars.
The kinetic energy of liberated electrons is measured by experiments involving the photoelectric effect, not by a photometer.
The frequency and wavelength of light are measured using devices such as spectrometers or diffraction gratings.
Therefore, the correct function of a photometer is to measure the intensity of light.
Answer:B. Intensity of light