Assertion : At constant temperature PV vs P plot for real gases is not a straight line .
Reason : In the curves of dihydrogen and helium , as the pressure increases the value of PV also increases .

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 .

Explanation

To solve the question regarding the assertion and reason about the PV vs P plot for real gases, we will break down the concepts step by step.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that at constant temperature, the PV vs P plot for real gases is not a straight line.
- This is indeed true because real gases do not behave ideally under all conditions, especially at high pressures and low temperatures.

**Hint**: Recall that ideal gases follow the ideal gas law (PV = nRT), which predicts a linear relationship between PV and P. Real gases deviate from this behavior.

2. **Understanding the Reason**:
- The reason given is that for the curves of dihydrogen and helium, as the pressure increases, the value of PV also increases.
- This is also true. For these light gases, as pressure increases, the product PV tends to increase due to their low molecular mass and the effects of intermolecular forces.

**Hint**: Consider how molecular weight and intermolecular forces affect the behavior of gases under varying pressures.

3. **Evaluating the Relationship**:
- While both the assertion and the reason are true, the reason does not provide a complete explanation for the assertion. The assertion speaks about the general behavior of real gases, while the reason specifically addresses only dihydrogen and helium.

**Hint**: Think about whether the reason explains the broader concept of real gas behavior or just specific cases.

4. **Conclusion**:
- Since both statements are true but the reason does not adequately explain the assertion, the correct answer is that both assertion and reason are true, but the reason is not the correct explanation of the assertion.

**Final Answer**: The correct option is **B**: Both assertion and reason are true, but the reason is not the correct explanation of the assertion.