Assertion (A): Sodium metal is softer than potassium metal.
Reason (R ): Metallic bond in potassium is weaker than in sodium.

Options

A. If both (A) and (R ) are correct and (R ) is the correct explanation of (A).
B. If both (A) and (R ) are correct, but (R ) is not the correct explanation of (A).
C. If (A) is correct, but (R ) is incorrect.
D. If (A) is incorrect, but (R ) is correct.

Explanation

To solve the assertion and reasoning question, we will analyze both the assertion (A) and the reason (R) step by step.

### Step 1: Analyze the Assertion (A)
The assertion states that "Sodium metal is softer than potassium metal."

- **Fact Check**: In reality, potassium is softer than sodium. Potassium has a larger atomic size, which leads to a less compact arrangement of atoms. Therefore, the assertion is **false**.

### Step 2: Analyze the Reason (R)
The reason states that "Metallic bond in potassium is weaker than in sodium."

- **Understanding Metallic Bonding**: The strength of metallic bonds is influenced by the size of the atoms. As the atomic size increases, the distance between the nucleus and the delocalized electrons also increases, leading to weaker metallic bonds.
- **Comparison**: Since potassium has a larger atomic size than sodium, the metallic bond in potassium is indeed weaker than that in sodium. Therefore, the reason is **true**.

### Step 3: Conclusion
- Since the assertion (A) is false and the reason (R) is true, we can conclude that the correct answer is that the assertion is incorrect while the reason is correct.

### Final Answer
- Assertion (A) is false.
- Reason (R) is true.
- Therefore, the correct option is that A is false and R is true.

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