Assertion: Both `12 g`. of carbon and `27 g`. of aluminium will have `6.02xx10^(23)` atoms.
Reason: Gram atomic mass of an element contains Avogadro's number of atoms.

Options

A. Both Assertion and Reason are true and Reason is the correct explanation of Assertion
B. Both Assertion and Reason are true but Reason is not a correct explanation of Assertion
C. Assertion is true but Reason is false
D. Assertion is false but Reason is true

Explanation

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

### Step-by-Step Solution:

1. **Understanding the Assertion:**
- The assertion states that both 12 g of carbon and 27 g of aluminum will have \(6.02 \times 10^{23}\) atoms.
- This is based on the concept of molar mass and Avogadro's number.

2. **Calculating for Carbon:**
- The molar mass (gram atomic mass) of carbon (C) is 12 g/mol.
- To find the number of moles in 12 g of carbon:
\[ \text{Number of moles} = \frac{\text{mass in grams}}{\text{molar mass}} = \frac{12 \text{ g}}{12 \text{ g/mol}} = 1 \text{ mole} \]
- Since 1 mole of any substance contains \(6.02 \times 10^{23}\) atoms (Avogadro's number), the number of atoms in 12 g of carbon is:
\[ 1 \text{ mole} \times 6.02 \times 10^{23} \text{ atoms/mole} = 6.02 \times 10^{23} \text{ atoms} \]

3. **Calculating for Aluminum:**
- The molar mass of aluminum (Al) is 27 g/mol.
- To find the number of moles in 27 g of aluminum:
\[ \text{Number of moles} = \frac{27 \text{ g}}{27 \text{ g/mol}} = 1 \text{ mole} \]
- Similarly, the number of atoms in 27 g of aluminum is:
\[ 1 \text{ mole} \times 6.02 \times 10^{23} \text{ atoms/mole} = 6.02 \times 10^{23} \text{ atoms} \]

4. **Conclusion on Assertion:**
- Both 12 g of carbon and 27 g of aluminum indeed contain \(6.02 \times 10^{23}\) atoms.

5. **Understanding the Reason:**
- The reason states that the gram atomic mass of an element contains Avogadro's number of atoms.
- This is correct because the gram atomic mass (molar mass) corresponds to the mass of one mole of that element, which is defined to contain \(6.02 \times 10^{23}\) atoms.

6. **Final Evaluation:**
- Since both the assertion and the reason are correct, and the reason correctly explains the assertion, we conclude that the answer is:
- **Both Assertion and Reason are correct, and Reason explains Assertion.**

### Final Answer:
- The correct answer is **A**: Both Assertion and Reason are correct, and Reason explains Assertion.