For each of the equation four choices have been provided .select the correct alternative
In case of an incense stick or an agarbati the smoke at the lighted end of stick moves in upward direction it is because

Options

A. the cool air below the lighted end moves to take the place of hot air above the lighted end.
B. the air at the hot end is more dense.
C. it is natural for the smoke to move
D. the smoke is repelled by the gravity of earth.

Answer

A

Explanation

In case of an incense stick, the air at the lighted end is hot, and hence, volume increases and density decreases, so, it rises up (moves up).
(or)
The air at the hot end is at a higher temperature, so, its density is less and this lesser dense air rises up and more dense air occupies this place, so, it is due to convection of gases.