Assertion : For a certain fixed amount of gas the product PV is always constant
Reason : Real gases deviate from ideal behaviour of low pressure and high temperature

Options

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

Answer

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 for a certain fixed amount of gas, the product of pressure (P) and volume (V) is always constant.
- According to the ideal gas law, \( PV = nRT \), where \( n \) is the number of moles, \( R \) is the gas constant, and \( T \) is the temperature.
- This equation shows that the product \( PV \) is not always constant; it varies with temperature (T). Therefore, the assertion is **false**.

2. **Understanding the Reason**:
- The reason states that real gases deviate from ideal behavior at low pressure and high temperature.
- In reality, real gases deviate from ideal behavior at **high pressure** and **low temperature**. At high pressures, the volume of gas particles becomes significant, and at low temperatures, intermolecular forces become more pronounced.
- Therefore, the reason is also **false**.

3. **Conclusion**:
- Since both the assertion and the reason are false, the correct option is that both statements are false.

### Final Answer:
Both the assertion and the reason are false.