An unknown metal X when placed in copper sulphate solution, red brown pieces of copper fall to the bottom of the test tube. When metal X is placed in aluminium sulphate solution, no change is observed. Metal X can be

Options

A. Sodium
B. Potassium
C. Iron
D. Calcium.

Explanation

To determine the identity of the unknown metal X based on the given observations, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Reaction with Copper Sulphate**:
- When metal X is placed in copper sulphate solution, red-brown pieces of copper are observed to fall to the bottom of the test tube. This indicates that metal X is more reactive than copper.
- The reaction can be represented as:
\[ \text{X} + \text{CuSO}_4 \rightarrow \text{Cu} + \text{XSO}_4 \]
- Here, metal X displaces copper from copper sulphate.

2. **Understanding the Reaction with Aluminium Sulphate**:
- When metal X is placed in aluminium sulphate solution, no change is observed. This means that metal X is less reactive than aluminium.
- Therefore, metal X cannot displace aluminium from aluminium sulphate.

3. **Analyzing the Reactivity Series**:
- The reactivity series of metals from most reactive to least reactive is as follows:
- Potassium > Sodium > Calcium > Magnesium > Aluminium > Zinc > Iron > Lead > Hydrogen > Copper > Mercury > Silver > Gold
- From the first observation, we conclude that metal X must be above copper in the reactivity series.
- From the second observation, we conclude that metal X must be below aluminium in the reactivity series.

4. **Identifying Possible Metals**:
- The metals that are above copper but below aluminium in the reactivity series are:
- Zinc
- Iron
- Lead
- Therefore, the possible candidates for metal X are zinc, iron, and lead.

5. **Evaluating the Options**:
- If we analyze the options provided:
- **Sodium**: More reactive than aluminium (incorrect).
- **Potassium**: More reactive than aluminium (incorrect).
- **Iron**: Less reactive than aluminium and more reactive than copper (correct).
- **Calcium**: More reactive than aluminium (incorrect).
- The only metal that fits all criteria is **Iron**.

### Conclusion:
Thus, the unknown metal X can be identified as **Iron**.

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