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 solve the problem, we need to analyze the behavior of the unknown metal X when it is placed in two different solutions: copper sulfate and aluminum sulfate.

### Step-by-Step Solution:

1. **Understanding the Reaction with Copper Sulfate**:
- When metal X is placed in copper sulfate (CuSO₄) solution, red-brown pieces of copper fall to the bottom of the test tube. This indicates that metal X is more reactive than copper.
- The reaction can be represented as:
\[ \text{Metal X} + \text{CuSO}_4 \rightarrow \text{Metal XSO}_4 + \text{Cu} \]
- Since copper is displaced, it confirms that metal X is capable of replacing copper in the solution.

2. **Understanding the Reaction with Aluminum Sulfate**:
- When metal X is placed in aluminum sulfate (Al₂(SO₄)₃) solution, no change is observed. This means that metal X is less reactive than aluminum.
- If metal X were more reactive than aluminum, a reaction would occur, but since there is no reaction, we conclude that:
\[ \text{Metal X} + \text{Al}_2(SO_4)_3 \rightarrow \text{No reaction} \]

3. **Analyzing the Reactivity of Metals**:
- We need to determine which metal fits the criteria:
- Metal X must be more reactive than copper (to displace it from copper sulfate).
- Metal X must be less reactive than aluminum (to not react with aluminum sulfate).

4. **Evaluating the Options**:
- **Option 1: Sodium (Na)** - More reactive than aluminum. **(Incorrect)**
- **Option 2: Potassium (K)** - More reactive than aluminum. **(Incorrect)**
- **Option 3: Iron (Fe)** - More reactive than copper but less reactive than aluminum. **(Correct)**
- **Option 4: Calcium (Ca)** - More reactive than aluminum. **(Incorrect)**

5. **Conclusion**:
- The only metal that satisfies both conditions (more reactive than copper and less reactive than aluminum) is **Iron (Fe)**.

### Final Answer:
Metal X can be **Iron (Fe)**.