Diffraction increases with larger wavelength relative to aperture size

Steps:

• Diffraction is greater when wavelength λ ≥ aperture width d; here λ=0.50 m, d=1.0 m, so λ/d=0.5 (moderate diffraction).
• Sound speed v is constant, so λ=v/f; changes in f alter λ inversely.
• To increase diffraction, increase λ (or decrease d) to make λ/d larger.
• Evaluate options: only halving f doubles λ, increasing λ/d.

Why C is correct:

• Halving frequency doubles λ (λ=v/f), increasing λ/d from 0.5 to 1.0 for more diffraction per Huygens' principle.

Why the others are wrong:

• A: Doubling amplitude increases intensity but does not affect diffraction angle or extent.
• B: Doubling width halves λ/d, reducing diffraction.
• D: Halving period doubles frequency (T=1/f), halving λ and decreasing diffraction.

Final answer: C