A : `CaCO_(3)` requires more temperature than `MgCO_(3)` for decomposition.
R : Group II metal carbonates on decomposition gives respective oxide and `CO_(2)`

Options

A. If both Assertion & Reason are true and the reason is the correct explanantion of the assertion, then mark (1).
B. If both Assertion & Reason are true and the reason is the correct explanantion of the assertion, then mark (2).
C. If Assertion is true statement but Reason is false. Them mark (3).
D. If both Assertion and reason are false statement, then mark (4).

Answer

To solve the question, we need to analyze both the assertion (A) and the reason (R) provided.

### Step 1: Analyze the Assertion (A)
The assertion states that "CaCO₃ requires more temperature than MgCO₃ for decomposition."

- **Explanation**: Calcium carbonate (CaCO₃) indeed requires a higher temperature for decomposition compared to magnesium carbonate (MgCO₃). This is due to the larger size of the calcium ion (Ca²⁺) compared to the magnesium ion (Mg²⁺). The larger ionic size of Ca²⁺ leads to a more stable lattice structure in CaCO₃, making it more thermally stable and requiring more heat to break down into calcium oxide (CaO) and carbon dioxide (CO₂).

### Step 2: Analyze the Reason (R)
The reason states that "Group II metal carbonates on decomposition give respective oxide and CO₂."

- **Explanation**: This statement is also true. When group II metal carbonates decompose upon heating, they produce their respective metal oxides and carbon dioxide gas. For example:
- CaCO₃ → CaO + CO₂
- MgCO₃ → MgO + CO₂

This is a general characteristic of group II metal carbonates.

### Step 3: Determine the Relationship Between A and R
Now we need to determine if the reason (R) correctly explains the assertion (A).

- While both statements are true, the reason does not specifically explain why CaCO₃ requires a higher temperature than MgCO₃ for decomposition. The reason discusses the general behavior of group II metal carbonates, but it does not address the specific thermal stability differences between CaCO₃ and MgCO₃.

### Conclusion
- **Assertion (A)**: True
- **Reason (R)**: True, but it does not correctly explain the assertion.

Thus, the correct answer is that both A and R are true, but R is not the correct reason for A.