Question

which of these is most likely to happen if a balloon is filled with hydrogen gas and then released in air

Answer 1

if a ballon is filled with hydrogen gas so as we know H gas have very low density or very light .So due to this ballon also become light and fly.

Answer 2

They rise up. As they go up, the atmospheric pressure decreases causing the balloons to expand. At some height it reaches a condition where the balloon skin cannot stretch any longer. The balloon pops.