​Smoke goes up because:​

Correct option is B

The correct answer is Warm air is lighter than cold air.

• Warm air is lighter than cold air:
  ○ Warm air is less dense than cold air because as air warms up, it expands and its molecules move farther apart.
  ○ Due to this decrease in density, warm air rises above the denser, colder air surrounding it.
  ○ Smoke, which consists of warm gases and particles, rises because it is carried by the upward-moving warm air.

Additional Information

• Warm air is denser than cold air:
  ○ This statement is incorrect because warm air is actually less dense than cold air. Denser air sinks below less dense air.
• Warm air has higher volume than cold air:
  ○ While warm air does expand and occupy a larger volume, the reason smoke goes up is specifically due to the decrease in density, not just the increase in volume.
• Warm air is heavier than cold air:
  ○ This statement is incorrect. Warm air is lighter (less dense), which is why it rises above the cooler, heavier (denser) air.