Which weighs more, 0.50 mole oxygen atoms or 4 mole of hydrogen atoms?

0.5 moles of oxygen weighs more than that of the 4 moles of hydrogen.

Explanation:

Atomic mas of oxygen = 16.0 g/mol

mass of 0.50 moles of oxygen atom =

Atomic mas of hydrogen = 1.0 g/mol

Mass of 4 moles of hydrogen atom =

0.5 moles of oxygen weighs more than that of the 4 moles of hydrogen.

altitude, density, pressure

air gets less dense the higher the altitude and also the air pressure is less as altitude rises.