Is air inside the balloon has weight?

Answer 1

Air has weight wherever it is. The weight of a jug full of air depends on the temperature

and pressure in the jug.

At sea-level pressure and 32 degrees, one pound of air fills about 92.7 gallons, and the

air in a 10-ft x 12-ft bedroom with a 7-ft ceiling represents about 67.8 pounds of weight.

Don't forget, though, that anything surrounded by fluid is buoyed up by a force

equal to the weight of the displaced fluid, and a room full of air displaces ... one

roomfull of air! So it 'floats', and winds up with a net weight of essentially zero.

(If you could suddenly heat all the air in the room, making it less dense than

the air around it, then the buoyant force would be more than its weight, and

it would want to rise. Then the room would be a "hot-air balloon".)