Assertion(A) One atomic mass unit is defined as one twelth of the mass of one carbon-12 atom.
Reason(R) Carbon-12 isotope is the most abundant isotope of carbon and has been chosen as standard.

Options

A. Both A and R are true and R is the correct explnanation of A.
B. Both A and R true but R is not the correct explanation of A.
C. A is true but R is false.
D. Both A and R are false.

Explanation

To solve the assertion-reason question, we will analyze both the assertion and the reason step by step.

### Step 1: Analyze the Assertion
**Assertion (A)**: One atomic mass unit is defined as one twelfth of the mass of one carbon-12 atom.

- **Definition of Atomic Mass Unit (AMU)**: The atomic mass unit (AMU) is indeed defined as one twelfth (1/12) of the mass of a carbon-12 (C-12) atom. This definition is widely accepted in chemistry and is used as a standard for measuring atomic masses of all other elements.

**Conclusion for Assertion**: The assertion is true.
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