Explanation
Statement I — Correct (conceptually).
Without the atmosphere, Earth would lose heat rapidly to space because there would be
no greenhouse effect. The average global temperature would fall to around
–18°C (compared to ~+15°C today).
The phrase
“everywhere below freezing” is technically an oversimplification, because temperatures would vary sharply — very hot on the sunlit side and extremely cold on the dark side. However, the statement is
conceptually correct as it refers to the
overall average condition of the planet, which would be below freezing and largely uninhabitable.
Statement II — Correct.
The atmosphere acts like a
heat-retaining blanket, trapping outgoing
infrared radiation and maintaining a
stable and life-supporting temperature — this is the greenhouse effect.
Statement III — Correct.
Gases such as
carbon dioxide, methane, and water vapour are effective
greenhouse gases because they absorb and re-radiate
infrared radiation, preventing excessive heat loss.
Thus,
all three statements are correct.