How does an acid–base indicator react when placed in an acidic solution?

it changes color.
it dissolves.
it increases the ph of the solution.
it releases hydroxide ions.

Option (a) is the correct answer.

Explanation:

An acid-base indicator is an indicator which changes color according to the pH of solution in which it is placed.

For example, phenolphthalein is an acid-base indicator.

Thus, we can conclude that out of the given options, an acid–base indicator react by changing color when placed in an acidic solution, is the correct option.