Which of the following is an example of a qualitative test?

Qualitative tests are designed to determine the presence or absence of a particular substance or attribute, rather than measuring the amount or concentration of that substance. In the context of the provided options, food allergy testing using skin prick tests serves as a clear example of a qualitative test.

When a skin prick test is conducted, the patient's skin is exposed to small amounts of potential allergens. The results are interpreted based on the presence or absence of a reaction—typically, swelling or redness at the site of the prick. This indicates whether the individual is allergic to the tested substances without measuring the exact levels of allergenic response.

In contrast, the other options involve quantitative measurements or determinations. For instance, pH testing involves measuring the acidity or alkalinity of a solution, thereby providing a quantitative value. Blood glucose level measurement determines the specific concentration of glucose in the blood, which is also a quantitative assessment. DNA quantification provides a measurement of the amount of DNA present, representing another quantitative test. Therefore, the skin prick test's focus on identifying the presence of allergies distinctly characterizes it as a qualitative test.