Fill in the blanks by using the correct word/term given in the brackets.
An acid _____ change the colour of phenolphthalein. (must/does not)

Explanation

To fill in the blank in the statement "An acid _____ change the colour of phenolphthalein," we need to understand the behavior of phenolphthalein in the presence of acids and bases.

1. **Understanding Phenolphthalein**: Phenolphthalein is a pH indicator that is colorless in acidic solutions (pH < 7) and turns pink in basic solutions (pH > 7).

2. **Behavior in Acidic Solutions**: When an acid is present, the pH of the solution is less than 7. In this case, phenolphthalein remains colorless.

3. **Conclusion**: Since an acid does not change the color of phenolphthalein (it stays colorless), we can conclude that the correct term to fill in the blank is "does not".

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