The buoyant force on the lead balloon was caused by the air molecules in the room and thus these air molecules will be hitting the surface of the balloon and those collisions will cause a force per unit area.
Answer: Option D
Explanation:
The term buoyant force is exerted mostly by objects getting fully or partially immersed in a fluid. This is the upward thrusting force exerted by the fluid on the bottom of the object to prevent the complete immersion of the object.
In other words, the buoyant force helps to keep the object floating. In case of balloon in air, the air pressure acts as the fluid which will be hitting the surface of balloon.
So, these collisions will prevent the balloon to fall down and to remain floating in air with an upward push from the collision of air molecules with the surface of balloon. So, the buoyant force acts on the lead balloon by collision of air molecules with the surface of balloon and pushing it in upward direction.
