Both Statement-I and Statement-II are correct, and Statement-II provides the correct explanation for Statement-I.
Statement-I is correct. The troposphere, the lowest layer of Earth's atmosphere where most weather phenomena occur, exhibits significant variation in its thickness. It is considerably thicker at the equator, typically around 16 to 18 km, compared to the poles, where its thickness is approximately 8 km. This difference is primarily due to the thermal expansion and uplift of air in the equatorial region.
Statement-II is correct. The equatorial region receives the maximum amount of solar radiation throughout the year. This intense heating of the Earth's surface and the overlying air causes the air to warm, become less dense, and rise vigorously. These strong vertical air movements are known as convectional currents. These currents effectively transport heat, moisture, and atmospheric gases to great heights within the atmosphere.
Statement-II explains Statement-I because the strong convectional currents at the equator, driven by intense solar heating, cause the air to expand and rise to higher altitudes. This upward movement pushes the boundary of the troposphere (the tropopause) to a greater height, thereby increasing the overall thickness of the troposphere in the equatorial region compared to the colder, subsiding air conditions prevalent at the poles.
Option (B) is incorrect because Statement-II directly explains the reason for the variation in tropospheric thickness described in Statement-I.
Option (C) is incorrect because Statement-II accurately describes the strong convectional activity at the equator, which is a fundamental atmospheric process.
Option (D) is incorrect because Statement-I correctly identifies the greater thickness of the troposphere at the equator compared to the poles.