How will a balloon filled with helium move? oxygen?

A balloon filled with helium will fly upward, since the density of helium is less than the density of air, filled with oxygen will fall, since its density is greater than that of air.

Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.