Answer: Helium exhibit less density as compared to oxygen and nitrogen thus the balloons floats in the mass of air.
Explanation:
Oxygen has an atomic mass of 15.994 and nitrogen has an atomic mass of 14. 006. The helium which is a noble gas has an atomic mass of 4. 002. This is indicative of the fact that the helium is less denser than the air containing oxygen and nitrogen. Thus as a result of this the helium floats on the air being lighter then the other components of air and hence, the helium balloons float in the air.
