Assertion: Pure water obtained from different sources always contains hydrogen and oxygen in the ratio of 1 : 8 by mass.
Reason: Molecular mass of water is 18.

Options

A. Assertion and reason both are correct statements and reason is correct explanation for assertion.
B. Assertion and reason both are correct statements but reason is not correct explanation for assertion.
C. Assertion is correct statements but reason is wrong statement.
D. Assertion is wrong statement but reason is correct statement.

Answer

To solve the question, we will analyze both the assertion and the reason provided, and evaluate their correctness and relationship.

### Step-by-Step Solution

1. **Understanding the Assertion**:
- The assertion states that pure water obtained from different sources always contains hydrogen and oxygen in the ratio of 1:8 by mass.
- To verify this, we need to consider the composition of water (H₂O). Water consists of 2 hydrogen atoms and 1 oxygen atom.

2. **Calculating the Mass Ratio**:
- The atomic mass of hydrogen (H) is approximately 1 g/mol. Since there are 2 hydrogen atoms, the total mass of hydrogen in water is:
\[ \text{Mass of H} = 2 \times 1 = 2 \text{ g/mol} \]
- The atomic mass of oxygen (O) is approximately 16 g/mol. Therefore, the total mass of oxygen in water is:
\[ \text{Mass of O} = 16 \text{ g/mol} \]
- Now, we can find the mass ratio of hydrogen to oxygen:
\[ \text{Mass ratio of H to O} = \frac{2}{16} = \frac{1}{8} \]
- This confirms that the assertion is correct.

3. **Understanding the Reason**:
- The reason states that the molecular mass of water is 18 g/mol.
- To calculate the molecular mass of water (H₂O):
\[ \text{Molecular mass of H₂O} = \text{Mass of H} + \text{Mass of O} = 2 + 16 = 18 \text{ g/mol} \]
- This statement is also correct.

4. **Analyzing the Relationship**:
- While both the assertion and the reason are correct, we need to determine if the reason provides a valid explanation for the assertion.
- The assertion discusses the mass ratio of hydrogen and oxygen in water, while the reason discusses the molecular mass of water. There is no direct link between the two statements that would make the reason an explanation for the assertion.

5. **Conclusion**:
- Both the assertion and the reason are correct statements, but the reason does not correctly explain the assertion. Therefore, the correct answer is:
- Assertion and reason are both correct statements, but the reason is not a correct explanation for the assertion.

### Final Answer
Assertion: True
Reason: True
Conclusion: Both are correct, but the reason is not the correct explanation for the assertion.

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