A student puts one big iron nail each in four test tubes containing solutions of zinc sulphate, aluminium sulphate, copper sulphate and iron sulphate. A reddish-brown coating was observed only on the surface of iron nail which was put in the solution of

Options

A. zinc sulphate
B. iron sulphate
C. copper sulphate
D. aluminium sulphate.

Explanation

To solve the problem step by step, let's analyze the situation with the iron nail and the different metal sulfate solutions.

### Step 1: Identify the solutions and their components
The student has four test tubes with the following solutions:
- Test Tube A: Zinc Sulphate (ZnSO₄)
- Test Tube B: Aluminium Sulphate (Al₂(SO₄)₃)
- Test Tube C: Copper Sulphate (CuSO₄)
- Test Tube D: Iron Sulphate (FeSO₄)

### Step 2: Understand the reactivity series
The reactivity series of metals helps us predict whether a reaction will occur when a metal is placed in a solution of another metal's salt. The order of reactivity from most reactive to least reactive is:
1. Aluminium
2. Zinc
3. Iron
4. Copper

### Step 3: Analyze each test tube for possible reactions
- **Test Tube A (Zinc Sulphate)**: Iron is less reactive than zinc, so no reaction will occur.
- **Test Tube B (Aluminium Sulphate)**: Iron is less reactive than aluminium, so no reaction will occur.
- **Test Tube C (Copper Sulphate)**: Iron is more reactive than copper, so a reaction will occur. Iron will displace copper from copper sulphate, leading to the formation of iron sulphate and the deposition of copper on the iron nail.
- **Test Tube D (Iron Sulphate)**: Since the metal and salt are the same (iron), no reaction will occur.

### Step 4: Identify the observable change
The reddish-brown coating observed on the iron nail indicates the deposition of copper. This occurs only in Test Tube C, where the iron nail is placed in copper sulphate solution.

### Conclusion
The reddish-brown coating was observed only on the surface of the iron nail which was put in the solution of **Copper Sulphate (CuSO₄)**.