If four balloons A, B, C and D are filled with hydrogen, oxygen, helium and nitrogen gases respectively and left in air, which balloon reaches to the highest distance from the Earth?

The ascent of a gas-filled balloon is determined by buoyancy, which depends on the density difference between the gas inside and the surrounding air. According to the principle of buoyancy, a balloon rises if its total density is lower than the atmospheric density [2]. The molecular weight of a gas is a primary determinant of its density; hydrogen (H2) has the lowest molecular weight (approximately 2 g/mol), followed by helium (He, ~4 g/mol), nitrogen (N2, ~28 g/mol), and oxygen (O2, ~32 g/mol). While nitrogen and oxygen are heavier gases that remain at the bottom of the atmosphere [1], hydrogen is the lightest and provides the maximum lifting force per unit volume. Consequently, Balloon A, filled with hydrogen, will experience the greatest upward buoyant force and reach the highest altitude compared to balloons filled with denser gases.

Sources

1. [2] Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 9: The Amazing World of Solutes, Solvents, and Solutions > 9.5.2 Effect of temperature on density > p. 147
2. [1] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 20: Earths Atmosphere > Permanent Gases of The Atmosphere > p. 271