A : Magnesium and Cesium gives blue colour in flame colouration.
R : Mg and Cs are of comparable size.

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 not 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 will analyze both the assertion (A) and the reason (R) provided.

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states that "Magnesium and Cesium give blue color in flame coloration."
- In flame tests, different elements produce characteristic colors when heated. However, Magnesium does not produce a flame color; it typically burns with a bright white light when ignited, and it does not impart a blue color to the flame. Cesium, on the other hand, does produce a blue color in flame tests.
- Therefore, the assertion is **incorrect** because it implies that both elements give a blue color, which is not true for Magnesium.

2. **Understanding the Reason (R)**:
- The reason states that "Mg and Cs are of comparable size."
- Magnesium (Mg) is an alkaline earth metal located in Group 2 of the periodic table, while Cesium (Cs) is an alkali metal located in Group 1.
- As we move down a group in the periodic table, the atomic size increases. Cesium is located lower in the periodic table than Magnesium, which means that Cesium has a larger atomic size compared to Magnesium.
- Therefore, the reason is also **incorrect** because Magnesium and Cesium are not of comparable size; in fact, Cesium is significantly larger than Magnesium.

3. **Conclusion**:
- Both the assertion (A) and the reason (R) are incorrect. Thus, the correct answer to the question is that both A and R are false.

### Final Answer:
Both assertion (A) and reason (R) are incorrect.

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