Greenhouse Effect

Without the greenhouse effect, Earth would be −18°C. With the natural greenhouse effect, Earth's average is +15°C.

The warming provided = $+15°C-(-18°C)=15+18=33°C$.

The natural greenhouse effect provides a warming of 33°C, making Earth habitable for life as we know it.

We need to find the temperature difference between Earth with the greenhouse effect (+15°C) and Earth without it (−18°C).

15°C is simply Earth's current average temperature — it is not the warming caused by the greenhouse effect. Eliminate this option.

18°C is the magnitude of the temperature without the greenhouse effect (−18°C), not the difference between the two values. Eliminate this option.

3°C is far too small — it does not result from any reasonable calculation using −18°C and +15°C. Eliminate this option.

$+15-(-18)=33°C$, so 33°C is the warming provided by the natural greenhouse effect.

For a molecule to absorb infrared radiation, its vibrations must cause a change in the distribution of electric charge (dipole moment). This depends on the molecular structure.

N₂ is a perfectly symmetrical two-atom molecule. When it vibrates, the charge distribution stays completely even — no change in dipole moment — so it cannot absorb infrared radiation.

CO₂ has a more complex, asymmetric structure. When its bonds bend and stretch, the charge distribution shifts, allowing it to absorb infrared radiation.

The correct explanation involves molecular symmetry and charge distribution, not abundance, type of light absorbed, or reflection.

We need the correct explanation for why N₂ is not a greenhouse gas but CO₂ is, at the molecular level.

The option stating N₂ is too abundant to absorb radiation is incorrect — abundance does not determine whether a gas absorbs infrared radiation. The ability to absorb IR depends on molecular structure.

The claim that N₂ absorbs visible light is incorrect — N₂ does not significantly absorb any of these common radiation types in the lower atmosphere.

N₂ does not reflect infrared radiation back into space — it simply does not interact with it. This option describes the wrong mechanism.

The correct answer correctly refers to N₂'s symmetry and lack of charge change during vibration, contrasted with CO₂'s complex structure that does allow infrared absorption.