Answer: Option (A) is the correct answer.
Step-by-step explanation:
When a fluid is heated then cold material (more dense) sinks at the bottom whereas hot material (less dense) rises at the top. Due to this mixing of materials there is formation of current which is known as convection current.
Thus, we can conclude that fluids rise if they are less dense than the matter around them is the property of matter that allows convection currents to form.