Which planet is hottest, Venus or Mercury?

The surface temperature of Mercury is completely regulated by its closeness to the Sun and is about 430 C ( 806 F) at local Noon. Because of the Greenhouse Effect on Venus, the surface temperature is regulated by the trapped infrared energy which cannot escape back into space to balance what it receives from the Sun as is the case for Mercury. This means that the surface temperature of Venus is far hotter than on Mercury, in the neighborhood of 472 C ( 882 F). So, even though it is twice as far from the Sun and received 1/4 as much sunlight, it is hotter than Mercury!