Diffraction spreading increases with larger wavelength relative to gap width Steps:

• Diffraction causes waves to spread through a gap, with angle θ ≈ λ/d (d = gap width).
• Given d > λ, initial spreading is minimal.
• Wave speed v is constant in a ripple tank, so λ = v/f.
• Decreasing f increases λ, raising λ/d and thus θ.

Why B is correct:

• Decreasing frequency increases wavelength via λ = v/f (v constant), increasing the ratio λ/d and diffraction angle.

Why the others are wrong:

• A: Small decrease in gap width has minimal effect on θ when d > λ initially.
• C: Increasing frequency decreases λ = v/f, reducing λ/d and θ.
• D: Barrier height does not affect waves passing through the gap.

Final answer: B