Which is required for convection to occur?

Must be in contact with the liquid

The temperature also has to be altered.

Explanation:

Convection cannot happen in a vacuum

Convection results from a change in density in the fluid

Answer: Convection requires a medium for heat to travel. Mainly, convection is the transfer of heat energy through fluids which are liquids and gases. Due to heat transfer or absorption the density of fluids changes and causes them to rise since they become less dense. So cooler particles sinks due to the fact that it is more dense.