Assertion: In isochoric process p-V graph is straight line parallel to p-axis.
Reason: In isochoric process density `rho` remains constant.

Options

A. If both Assertion and Reason are correct and Reason is the correct explanation of Assertion.
B. If both Assertion and Reason are correct but Reason is not the correct explation os Assertion.
C. If Assertionis true bur Reason is false.
D. If Assertion is false but Reason is true.

Explanation

To analyze the given assertion and reason, let's break down the concepts involved in an isochoric process.

### Step-by-Step Solution:

1. **Understanding Isochoric Process**:
- An isochoric process is defined as a thermodynamic process where the volume (V) remains constant. This means that no work is done by the system since work done (W) is given by W = PΔV, and ΔV = 0.

2. **Assertion Analysis**:
- The assertion states that in an isochoric process, the p-V graph is a straight line parallel to the p-axis.
- Since the volume is constant, the pressure (P) can change with temperature (T), but the volume does not change. Therefore, the p-V graph will indeed be a vertical line (parallel to the p-axis) at the constant volume value.

3. **Reason Analysis**:
- The reason states that in an isochoric process, the density (ρ) remains constant.
- While it is true that the volume does not change, the density of a substance is defined as ρ = m/V, where m is the mass and V is the volume. Since the volume is constant but the temperature (and thus the pressure) can change, the density can also change if the mass remains constant. Therefore, the reason is incorrect.

4. **Conclusion**:
- The assertion is true because the p-V graph is indeed a straight line parallel to the p-axis in an isochoric process.
- The reason is false because the density does not necessarily remain constant in an isochoric process; it can vary with temperature changes if the substance undergoes a phase change or if the gas behaves non-ideally.

### Final Answer:
- The correct answer is (b): Both assertion and reason are correct, but the reason is not the correct explanation for the assertion.