Q1. Which is the major cause of global warming?
A Re-radiation of U.V. rays by O2 and N2
B Re-radiation of I.R. rays by O2 and N2
C Re-radiation of U.V. rays by CO2 and H2O
D Re-radiation of I.R. rays by CO2 and H2O Correct
Explanation
Global warming is mainly linked with the greenhouse effect, in which gases such as carbon dioxide and water vapour absorb and re-radiate infrared radiation emitted by the Earth. Oxygen and nitrogen form most of the atmosphere, but they are not strong greenhouse gases because they do not effectively absorb infrared radiation. Ultraviolet radiation is primarily associated with incoming solar energy and ozone absorption, not the trapping of heat near the surface. Therefore, infrared re-radiation by carbon dioxide and water vapour matches the mechanism.