The correct option is that both Statement-I and Statement-II are correct, with Statement-II explaining Statement-I. This is because the troposphere is thicker at the equator due to the intense solar heating, which leads to stronger convection currents that not only heat the air but also cause it to rise to greater altitudes. In contrast, at the poles, the cooler temperatures result in weaker convection currents, leading to a thinner troposphere. This concept aligns with the understanding of atmospheric dynamics and circulation patterns that can be found in standard UPSC materials, emphasizing the relationship between temperature gradients and atmospheric structure.