Which of the following metal pairs on burning is moist air do not give smell of ammonia ?
`Mg, Ca, K, Li, Na, Al`

Options

A. `Mg, K`
B. `Ca, Na`
C. `K, Na`
D. `Li, Al`

Answer

To solve the question of which metal pairs do not give the smell of ammonia when burned in moist air, we can analyze the reactions of each metal with nitrogen and water.

### Step-by-Step Solution:

1. **Understanding the Reaction**:
When metals react with moist air (which contains oxygen and nitrogen), they can form metal nitrides. These nitrides can further react with water to produce metal hydroxides and ammonia (NH₃). The presence of ammonia is what gives the characteristic smell.

2. **Analyzing Each Metal**:
- **Magnesium (Mg)**:
- Reaction with nitrogen:
\[ 3Mg + N_2 \rightarrow Mg_3N_2 \]
- Reaction with water:
\[ Mg_3N_2 + 6H_2O \rightarrow 3Mg(OH)_2 + 2NH_3 \]
- **Conclusion**: Produces ammonia.

- **Calcium (Ca)**:
- Reaction with nitrogen:
\[ 3Ca + N_2 \rightarrow Ca_3N_2 \]
- Reaction with water:
\[ Ca_3N_2 + 6H_2O \rightarrow 3Ca(OH)_2 + 2NH_3 \]
- **Conclusion**: Produces ammonia.

- **Lithium (Li)**:
- Reaction with nitrogen:
\[ 6Li + N_2 \rightarrow 2Li_3N \]
- Reaction with water:
\[ Li_3N + 3H_2O \rightarrow 3LiOH + NH_3 \]
- **Conclusion**: Produces ammonia.

- **Aluminum (Al)**:
- Reaction with nitrogen:
\[ 2Al + N_2 \rightarrow Al_2N_3 \]
- Reaction with water:
\[ Al_2N_3 + 6H_2O \rightarrow 2Al(OH)_3 + 3NH_3 \]
- **Conclusion**: Produces ammonia.

- **Sodium (Na)**:
- Sodium does not react with nitrogen under normal conditions, hence:
\[ \text{No reaction with } N_2 \]
- **Conclusion**: Does not produce ammonia.

- **Potassium (K)**:
- Similar to sodium, potassium does not react with nitrogen under normal conditions:
\[ \text{No reaction with } N_2 \]
- **Conclusion**: Does not produce ammonia.

3. **Final Conclusion**:
The metals that do not give the smell of ammonia when burned in moist air are Sodium (Na) and Potassium (K).

### Answer:
**Sodium (Na) and Potassium (K)** do not give the smell of ammonia.