Concept:Convection in a liquid is caused by changes in density when different parts of the liquid are heated.
Explanation:When a liquid is heated, it expands.
The heated liquid occupies a larger volume for the same mass.
Therefore, its density becomes lower than that of the surrounding cooler liquid.
The less dense, warmer liquid rises upward.
The cooler, denser liquid sinks downward to replace it.
This continuous movement creates a convection current.
The convection current transfers heat from the hot region to the cooler region.
So the main cause of convection in a liquid is the variation of density with temperature.
It is not mainly due to latent heat of vaporization.
It is also not simply due to increased molecular vibration about the mean position.
Both expansion and density change happen together, but the density difference is what drives the liquid motion.
Answer:C. Variation of density of the liquid