Which of the following will determine whether the given colourless liquid is water or not ?

Options

A. smelling
B. Tasting
C. Phenolphthalein
D. Adding a pinch of anhydrous `CuSO_(4)`

Answer

To determine whether the given colorless liquid is water or not, we can analyze each option provided:

1. **Smelling**:
- Water is a colorless and odorless liquid. However, there are many other colorless liquids that also do not have a particular smell. Therefore, smelling the liquid will not provide a definitive answer, as it could be another odorless liquid.

2. **Tasting**:
- Tasting the liquid is not a safe method. Many colorless liquids, including acids and toxic substances, can be harmful if ingested. Therefore, tasting is not a reliable or safe way to identify the liquid.

3. **Adding Phenolphthalein**:
- Phenolphthalein is an acid-base indicator that turns pink in basic solutions and remains colorless in neutral and acidic solutions. Since water is neutral (pH 7), adding phenolphthalein to the liquid would not cause any color change. However, this does not confirm that the liquid is water, as other neutral liquids would also yield the same result.

4. **Adding a Pinch of Anhydrous Copper Sulfate (CuSO4)**:
- Anhydrous copper sulfate is a white solid that turns blue when it absorbs water and forms hydrated copper sulfate (CuSO4·5H2O). If the colorless liquid is indeed water, adding a pinch of anhydrous copper sulfate will result in a blue solution, confirming the presence of water. This is a reliable method to determine if the liquid is water.

**Conclusion**: The most effective method to determine whether the given colorless liquid is water is by adding a pinch of anhydrous copper sulfate. If the solution turns blue, it indicates that the liquid is water.

**Final Answer**: D. Adding a pinch of anhydrous copper sulfate.

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