Question

how is venus hotter than mercury even if mercury is the closest to the sun?

Answer 1

 Its atmosphere is primarily composed of carbon dioxide - the primary green house gas  which acts like a one-way door. The solar heat enters, but it cannot leave.

Answer 2

venus is hotter than mercury because venus is having thicker atmosphere which mainly contains carbon dioxide which is a green house gas which traps sun's heat and make the planet hot.