X and Y are two metals. When burnt in air, X forms only oxide while Y forms oxide and nitride. The metals X and Y may be:

Options

A. Ca and Mg
B. Na and Mg
C. Li and Na
D. Na and K

Answer

To solve the problem, we need to identify two metals, X and Y, based on their reactions when burnt in air. Metal X forms only an oxide, while metal Y forms both an oxide and a nitride.

### Step-by-Step Solution:

1. **Understanding the Reactions**:
- When metals burn in air, they primarily react with oxygen to form oxides. Additionally, some metals can react with nitrogen to form nitrides.
- We need to find one metal (X) that only forms an oxide and another metal (Y) that forms both an oxide and a nitride.

2. **Analyzing the Options**:
- **Option 1: Calcium (X) and Magnesium (Y)**:
- Calcium reacts with oxygen to form CaO (oxide) and with nitrogen to form Ca3N2 (nitride).
- Magnesium reacts with oxygen to form MgO (oxide) and with nitrogen to form Mg3N2 (nitride).
- Here, both metals form oxides and nitrides, so this option is not valid.

- **Option 2: Sodium (X) and Magnesium (Y)**:
- Sodium reacts with oxygen to form Na2O (oxide) and does not react with nitrogen.
- Magnesium reacts with oxygen to form MgO (oxide) and with nitrogen to form Mg3N2 (nitride).
- Here, sodium (X) forms only an oxide, and magnesium (Y) forms both an oxide and a nitride. This option is valid.

- **Option 3: Lithium (X) and Sodium (Y)**:
- Lithium reacts with oxygen to form Li2O (oxide) and with nitrogen to form Li3N (nitride).
- Sodium reacts with oxygen to form Na2O (oxide) and does not react with nitrogen.
- Here, lithium forms both an oxide and a nitride, so this option is not valid.

- **Option 4: Sodium (X) and Potassium (Y)**:
- Sodium reacts with oxygen to form Na2O (oxide) and does not react with nitrogen.
- Potassium reacts with oxygen to form K2O (oxide) and does not react with nitrogen.
- Both sodium and potassium form only oxides, so this option is not valid.

3. **Conclusion**:
- The only valid pair that meets the criteria is **Sodium (X)**, which forms only an oxide, and **Magnesium (Y)**, which forms both an oxide and a nitride. Therefore, the answer is **Option 2: Sodium and Magnesium**.