Phase difference requires path length info Steps:

• Phase difference φ = (2π/λ) × path difference, where λ is wavelength.
• Without positions of X and Y or path lengths from source, calculate no specific φ.
• Waves in ripple tank are typically circular; phase depends on radial distances.
• Constant frequency implies same speed, but no distances given to find φ. Not enough information to determine phase difference.

Why D is correct:

• Cannot confirm; lacks path difference data tying to 270° (3/4 λ).

Why the others are wrong:

• A: No basis for 45° (1/8 λ).
• B: No basis for 135° (3/8 λ).
• C: No basis for 180° (1/2 λ), common but unstated here.

Final answer: Not enough information.