A mirage on a hot road forms because the air near the hot surface is rarer than the air above it. What does the refractive index of air do as height increases in such conditions?

1. Hot air near the road is less dense (rarer) than the cooler air higher up. 2. A denser medium has a higher refractive index, so the cooler upper air has a higher index. 3. The chapter states the refractive index of air keeps increasing as we go to increasing heights, which curves the distant light and creates the mirage. 4. A constant or zero refractive index would produce no mirage, so those distractors fail. _Source: Balbharati (Maharashtra Board) Class 10 Science & Technology, Ch 6 "Refraction of Light", p.85_