Smoke movement driven by heat-induced air currents

Steps:

• Smouldering rope generates heat at the box opening, warming nearby air.
• Warm air becomes less dense and rises, creating a low-pressure area.
• Cooler air from inside the box flows in to replace it, forming convection currents.
• These currents carry smoke into the box, explaining the observed direction.

Why A is correct:

• Convection involves heat transfer through fluid motion, where rising hot air creates currents that transport smoke particles.

Why the others are wrong:

• B: Free electrons enable electrical conduction in metals, unrelated to smoke or air flow.
• C: Radiation transfers heat via electromagnetic waves without moving matter like smoke.
• D: Molecular vibration represents internal kinetic energy but does not cause bulk fluid movement.

Final answer: A