A student was studying reactions of metals with dilute NaOH at room temperature. The student took dilute NaOH in four different test tubes and added copper powder to test tube A, zinc dust to test tube B, aluminium powder to test tube C and iron powder to test tube D and observed effervesce in ________.

Options

A. Test tubes A & B
B. Test tubes B & C
C. Test tubes C & D
D. Test tubes A & D

Explanation

To solve the question, we need to analyze the reactions of the metals with dilute NaOH (sodium hydroxide) and determine where effervescence occurs.

### Step-by-Step Solution:

1. **Identify the Metals and Their Reactions:**
- Test tube A: Copper powder (Cu)
- Test tube B: Zinc dust (Zn)
- Test tube C: Aluminium powder (Al)
- Test tube D: Iron powder (Fe)

2. **Understand the Reactivity of Each Metal with Dilute NaOH:**
- **Copper (Cu):** Copper does not react with dilute NaOH at room temperature. It only reacts with NaOH in the presence of oxygen or when it is in the form of a salt.
- **Zinc (Zn):** Zinc reacts with dilute NaOH to produce sodium zincate and hydrogen gas. The reaction is:
\[ \text{Zn} + 2 \text{NaOH} \rightarrow \text{Na}_2\text{ZnO}_2 + \text{H}_2 \uparrow \]
- **Aluminium (Al):** Aluminium also reacts with dilute NaOH, producing sodium aluminate and hydrogen gas. The reaction is:
\[ 2 \text{Al} + 2 \text{NaOH} + 6 \text{H}_2\text{O} \rightarrow 2 \text{Na}_3\text{AlO}_3 + 3 \text{H}_2 \uparrow \]
- **Iron (Fe):** Iron does not react with dilute NaOH at room temperature. It requires a strongly basic solution to react.

3. **Determine Where Effervescence Occurs:**
- Effervescence is observed when hydrogen gas is produced. From the reactions above, effervescence will occur in:
- Test tube B (Zinc with NaOH)
- Test tube C (Aluminium with NaOH)

4. **Conclusion:**
- The student will observe effervescence in test tubes B (Zinc) and C (Aluminium).

### Final Answer:
Effervescence is observed in test tubes B and C.