Assertion (A): Atomic mass of potassium is 39.
Reason (R ): An atom of postassium is 39 times heavier than `1//2th` of the mass of carbon atom `(C^(12))`.

Options

A. If both (A) and (R ) are correct and (R ) is the correct explantion for (A)
B. If both (A) and (R ) are correct but (R ) is not the correct explantion for (A)
C. If (A) is correct but (R ) is incorrect.
D. If (A) and (R ) are incorrect.

Explanation

To solve the question, we need to analyze both the assertion and the reason provided.

### Step 1: Understanding the Assertion
The assertion states that the atomic mass of potassium (K) is 39.

- **Fact Check**: The atomic mass of potassium is indeed approximately 39 amu (atomic mass units). This is a standard value found on the periodic table.

### Step 2: Understanding the Reason
The reason states that an atom of potassium is 39 times heavier than 1/12th of the mass of a carbon-12 atom.

- **Explanation**: The atomic mass unit (amu) is defined as 1/12th of the mass of a carbon-12 atom. Therefore, if the atomic mass of potassium is 39 amu, it means that one atom of potassium is 39 times heavier than 1/12th of the mass of a carbon-12 atom.

### Step 3: Conclusion
Both the assertion and the reason are correct. The reason correctly explains the assertion.

- **Final Statement**: Therefore, we conclude that both the assertion (A) and the reason (R) are correct, and the reason is a correct explanation for the assertion.

### Answer:
Both assertion and reason are correct, and the reason is the correct explanation for the assertion.

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