If Samir is holding a helium-filled balloon on a string and he lets go of the string outdoors where there is no wind, what happens to the helium-filled balloon and why?

Respond very briefly.
The helium-filled balloon will ascend into the air once Samir releases the string. This occurs because helium is lighter than air, meaning its density is less than the density of the atmosphere. The buoyant force, which acts upward on objects immersed in a fluid (in this case, the fluid is air), exceeds the downward force of gravity on the balloon, causing it to rise. The absence of wind means that there are no horizontal forces to push the balloon sideways, so it moves directly upward.