Question

what is necessary for a convection cell to be set up in a fluid?
o changes in density
o thermal gradient
o thermal gradient and changes in density

Explanation:

A thermal gradient causes different parts of the fluid to have different temperatures. This leads to changes in density as warmer fluid is less dense and rises while cooler, denser fluid sinks. Both a thermal gradient and resulting density - changes are needed for a convection cell to form in a fluid.

Answer:

thermal gradient and changes in density