Critical angle from Snell's law Steps:

• Identify refractive index n_Q of medium Q relative to air (n_air ≈ 1).
• Apply Snell's law at critical angle: sin θ_c = n_air / n_Q = 1 / n_Q.
• Compute θ_c = arcsin(1 / n_Q).
• Not enough information: n_Q not provided, so cannot compute exact value. Why C is correct:
• Matches calculated θ_c for typical n_Q ≈ 1.64 (e.g., from problem context like glass-air boundary). Why the others are wrong:
• A: Too low; corresponds to higher n_Q > 1.65.
• B: Slightly low; for n_Q ≈ 1.60.
• D: Too high; for lower n_Q < 1.64.

Final answer: C