Half of the oxygen in the oxygen bottle is used and the density becomes half of the original because the volume remains unchanged. But why does the volume remain unchanged

Half of the oxygen in the oxygen bottle is used and the density becomes half of the original because the volume remains unchanged. But why does the volume remain unchanged

Oxygen is filled in the bottle and takes up all the space, but the molecular spacing is small and the molecules are close to each other. Half of it is filled with the whole bottle, but the molecular spacing becomes larger and the volume remains unchanged

The volume of the medical oxygen cylinder is 100 cubic decimeters, and the density of the oxygen inside is 143 kg / m3. The mass of oxygen in the cylinder is () kg, and the weight of oxygen is () n

m=pV=143kg/m³×100×10-³=14.3kg
G=mg=14.3kg×10N/kg=143N

The original density of the oxygen bottle that has been rescuing the patient is p. when 2 / 3 oxygen is used for rescuing the patient, what is the density of the remaining oxygen in the bottle?

Density = mass m / volume V
In the problem, the volume of the oxygen cylinder is constant, so the volume is constant,
And two thirds of the oxygen is used, and one third is left, so the mass is one third of the original,
So density = one third of P