AI-generated practice question — model-generated for extra practice, not a previous-year CBSE board question.
Option A — Both A and R are true, and R is the correct explanation of A.
Hot air above fire is less dense, has a lower refractive index, and its continuously changing physical conditions cause irregular bending of light, making objects appear to waver.
Source: Chapter 10, Section 10.5 — Atmospheric Refraction
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The textbook explicitly states that hotter air is lighter (less dense) with a slightly lower refractive index, and since physical conditions are not stationary, the apparent position of objects fluctuates — exactly what R describes. Both A and R are correct, and R directly and fully explains A, so option A is the right choice. Examiners expect you to link "less dense → lower refractive index → changing conditions → irregular bending → wavering" as one connected chain of reasoning.