Venus surface is composed of carbon dioxide which is a green house gas so the heat enters and cannot leave. thus Venus has no water. so it is the hottest planet than mercury which lie closer to the sun
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Venus's atmosphere is some 100 times thicker than earth's atmosphere so when the sun rays hit the atmosphere  of Venus it heats up.Venus also has volcanoes like earth which also heats it up.Venus's average temperature is 461 degree celcius also know as 731 kelvin.Its atmosphere mainly consists of carbon dioxide which helps in traping heat.
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