Olfactory indicators are substances that have a distinct odor and change their odor when added to acidic or basic solutions. They work on the principle that when an acid or base is added to them, different odors can be detected in bases, whereas the odor remains the same in acids. These indicators are used to detect the presence of acids or bases in a solution by smelling the odor change.

Some properties of olfactory indicators include:

• They have a distinct odor.
• They change their odor in acidic or basic solutions.
• They aid in detecting the presence of acids or bases in a solution.

An example of an olfactory indicator is vanilla extract. When added to an acidic solution, it retains its characteristic vanilla odor. However, when added to a basic solution, it loses its vanilla odor and acquires a soapy odor.