As a hot air balloon rises from 0 (zero) kilometers to 6 kilometers above sea level which of the following happens? air density remains the same.

air density decreases.

air density increases.

air temperature increases.

The fire makes the air density decrease. If you are 6 km high, you would have trouble breathing. The fire in the hot air balloon would start to die down that high, the fire keeps the air less dense which makes the big cloth stay like a big balloon. If you were that high, the fire would die down and you’ll fall to the ground at very high speeds.