A: The phase difference between any two points on a wavelength is zero.
R:Corresponding to a beam of parallel rays of light the wavefronts, are planes parallel to one another.

Options

A. IF both Assertion & Reason are true and the reason is the correct explanation of the assertion, then mark (1).
B. If both Assertion & Reason are true but the reason is not the correct explanation of the assertion, then mark(2)
C. IF Assertion is true statement but Reason is false then mark(3)
D. If both Assertion and Reason are false statements, then mark (4)

Answer

To solve the question, we need to analyze both the assertion (A) and the reason (R) given in the problem.

### Step 1: Analyze the Assertion (A)
The assertion states: "The phase difference between any two points on a wavelength is zero."

1. **Understanding Phase Difference**:
- The phase difference between two points in a wave is defined as the difference in the phase of the wave at those two points.
- For any two points that are separated by a distance equal to the wavelength (λ), the phase difference is 2π radians, which corresponds to one complete cycle of the wave.

2. **Conclusion about Assertion**:
- The assertion is **false** because the phase difference between two points on a wavelength is not zero; it is 2π for points that are one wavelength apart.

### Step 2: Analyze the Reason (R)
The reason states: "Corresponding to a beam of parallel rays of light, the wavefronts are planes parallel to one another."

1. **Understanding Wavefronts**:
- A wavefront is defined as the surface over which an oscillation has a constant phase.
- For a beam of parallel rays of light, the wavefronts are indeed planar and parallel to each other, as they propagate in the same direction.

2. **Conclusion about Reason**:
- The reason is **true** because parallel rays of light create wavefronts that are planes and parallel to one another.

### Step 3: Determine the Relationship
Now we need to determine if there is a relationship between the assertion and the reason.

1. **Relationship Analysis**:
- The assertion and the reason are both true statements, but they pertain to different aspects of wave optics.
- The assertion discusses phase difference, while the reason discusses the nature of wavefronts for parallel rays.

### Final Conclusion
Based on the analysis:
- Assertion (A) is **false**.
- Reason (R) is **true**.
- There is no direct relationship between the two.

### Answer
The correct answer is: **Option 2** (Both A and R are true, but R is not the correct explanation of A).