Why is water densest 40 degree celsius

Which process does not require the presence of a physical substance in order to transfer heat? air in the atmosphere is heated by the ground. this warm air then rises, and cooler air falls. this is an example of what type of process? how is conduction different from radiation?

How have the greenhouse gasses increased from the year 2000 to 2018

Which formula can be used to calculate the molar mass of hydrogen peroxide