Which of the following is a qualitative test used in organic chemistry?

A qualitative test in organic chemistry is designed to identify the presence or absence of specific compounds or functional groups without providing quantitative information about their concentration or amount. Color reactions serve as a classic example of a qualitative test, as they involve observing changes in color that indicate the presence of certain functional groups or compounds when a reagent is added. For instance, a color change may occur in the presence of aldehydes, ketones, or certain metals, helping chemists to determine the nature of the substance being tested.

In contrast, other methods such as mass spectrometry and gas chromatography primarily provide quantitative data, as they give detailed information about the molecular weight and composition of compounds rather than solely indicating the presence of a compound. Titration, while it can sometimes be used qualitatively (for example, to determine if an endpoint was reached), is fundamentally a quantitative technique used to calculate the concentration of a solute in a solution.

Thus, color reactions stand out as a pure qualitative method, allowing chemists to ascertain the identity of compounds through observable changes without measuring amounts.