Hi! Here’s a simple way to think about Venus:
1. Venus has a super-thick blanket of gas around it. That blanket is mostly a gas called carbon dioxide. It traps the Sun’s heat, kind of like how a blanket keeps you warm at night. This trapped heat makes Venus very hot.
2. Venus also has many volcanoes. Volcanoes form when very hot rock (magma) from inside the planet pushes up and comes out as lava. Over a long time, this made the planet’s surface full of volcanoes and hot rock.
So, because of the thick gas blanket that traps heat and all the volcanic activity, Venus is the hottest planet.