Final answer:
The amount of light absorbed by a compound at a certain wavelength is proportional to its concentration in solution, which is useful for quantitative analysis. The correct option is (C).
Step-by-step explanation:
The absorption of light energy by a molecular species can be used for quantitative analysis because the amount of light energy absorbed at a particular wavelength by a compound in solution is proportional to its concentration in that solution.
The correct answer to the question is therefore C) Concentration.
This is due to the fact that molar absorptivity or extinction coefficient (ɛ) is a characteristic value for a given compound, which when divided by the concentration of the sample, can be used to calculate the absorbance and determine the concentration of a sample of known path length, commonly 1 cm.