Which planet has very high surface temperature mainly due to its dense atmosphere?

Correct answer: Venus

Direct answer: Option A, Venus, is correct. Venus has the hottest average surface temperature among the planets, even though Mercury is closer to the Sun. The key concept is the greenhouse effect. Venus has a very dense atmosphere containing much carbon dioxide. Sunlight enters, the surface becomes warm, and outgoing heat is trapped by the atmosphere instead of escaping easily. The reasoning is: dense atmosphere; strong trapping of heat; very high surface temperature. Option A is correct because Venus combines a thick atmosphere with an extreme greenhouse effect. Option B, Uranus, is a distant ice giant and has a very cold atmosphere, not the hottest surface. Option C, Mercury, is closest to the Sun but has almost no substantial atmosphere, so it cannot retain heat efficiently; its temperatures also vary greatly. Option D, Mars, has a thin atmosphere and is generally cold. Memory cue: closest does not always mean hottest—Venus is hottest because its atmosphere traps heat.