Explanation

Venus is hotter than Mercury because it has a much thicker atmosphere. Mercury is closer to the Sun but it has a very thin atmosphere and all the heat trapped goes out in space, while Venus with its much thicker atmosphere holds all the heat it gets. Venus is hotter due to the greenhouse effect: Venus has an atmosphere about ninety times thicker than that of Earth, and made almost entirely of carbon dioxide, which is one of the gasses that causes the greenhouse effect on Earth. On the other hand, Mercury’s atmosphere contains small amounts of hydrogen, helium, and oxygen. So, the heat received can be emitted as well. This is the reason why Venus is hotter than Mercury.