Convection Driven by Density Changes Steps:

• Heat the center base, warming water directly above.
• Warm water expands and becomes less dense than surrounding cooler water.
• Less dense warm water rises, displacing cooler water.
• Cooler, denser water from sides sinks to the heated area, establishing circulation.

Why B is correct:

• Convection occurs when fluids move due to density differences from temperature changes, as per the principle that warmer fluids are buoyant and rise.

Why the others are wrong:

• A: Expansion reduces density, causing rise, but the statement ignores density's role.
• C: Side water falls because it is cooler and denser, not less dense.
• D: Identical to A; focuses on expansion without mentioning density.

Final answer: B