What do you observe when you add a few drops of acetic acid to a test tube containing.
(a) phenolphthalein (b) distilled water (c) universal indicator (d) sodium hydrogen carbonate.

Explanation

To solve the question regarding the observations when adding acetic acid to different substances, we will analyze each case step by step.

### Step-by-Step Solution:

1. **Adding Acetic Acid to Phenolphthalein:**
- **Observation:** When a few drops of acetic acid (CH₃COOH) are added to phenolphthalein, there is no color change. The solution remains colorless.
- **Reason:** Phenolphthalein is an acid-base indicator that changes color in basic solutions but remains colorless in acidic solutions. Since acetic acid is a weak acid, it does not trigger any color change.

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