Assertion : Atomic mass of aluminium is 27.
Reason : An atom of aluminium is 27 times heavier than 1/12th of the mass of carbon-12 atom.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion.
B. If both assertion and reason are true but reason is not the correct explanation of assertion.
C. If assertion is true but reason is false.
D. If both assertion and reason are false.

Answer

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

**Assertion:** The atomic mass of aluminium is 27.
**Reason:** An atom of aluminium is 27 times heavier than 1/12th of the mass of a carbon-12 atom.

### Step-by-Step Solution:

1. **Understanding Atomic Mass:**
- The atomic mass of an element is defined as the mass of an atom compared to a standard reference, which is usually taken as 1/12th the mass of a carbon-12 atom.

2. **Atomic Mass of Aluminium:**
- The atomic mass of aluminium is given as 27. This means that one atom of aluminium weighs 27 times more than 1/12th of the mass of a carbon-12 atom.

3. **Analyzing the Reason:**
- The reason states that an atom of aluminium is 27 times heavier than 1/12th of the mass of a carbon-12 atom. This is consistent with the definition of atomic mass.

4. **Conclusion:**
- Since the assertion states that the atomic mass of aluminium is 27, and the reason correctly explains that this means aluminium is 27 times heavier than 1/12th of the mass of a carbon-12 atom, both the assertion and the reason are true.

### Final Answer:
Both the assertion and the reason are true, and the reason correctly explains the assertion.

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