A sample of oxygen gas is sealed in container X. A sample of hydrogen gas is sealed in container Z. Both samples have the same volume, temperature,

and pressure. Which statement is true?

(1) Container X contains more gas molecules than container Z.

(2) Container X contains fewer gas molecules than container Z.

(3) Containers X and Z both contain the same number of gas molecules.

(4) Containers X and Z both contain the same mass of gas.