Statement I: Insolation is greatest when the sun is directly overhead and the sun`s rays are vertical. Statement II: When the sun is lower in the sky, the same amount of solar energy spreads over a greater area of ground surface, so insolation is lower.

Statement I is correct as insolation, the incoming solar radiation per unit area, is at its maximum intensity when the sun is directly overhead at a 90° angle [1]. Statement II provides the physical explanation for this phenomenon: when the sun is lower in the sky (a smaller angle of incidence), the same beam of solar energy is distributed over a larger surface area, thereby reducing the energy received per unit area [1]. Additionally, lower sun angles force rays to travel through a greater depth of the atmosphere, increasing energy loss through scattering and absorption [3]. Because Statement II describes the geometric spreading of energy that directly causes the variation in intensity mentioned in Statement I, it serves as the correct explanation. This relationship between sun angle and surface area coverage is a fundamental driver of latitudinal and seasonal temperature variations.

Sources

1. [1] FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 8: Solar Radiation, Heat Balance and Temperature > Variability of Insolation at the Surface of the Earth > p. 68
2. [3] https://en.wikipedia.org/wiki/Effect_of_Sun_angle_on_climate