0.25 mole of hydrogen contains 1.5 * 10^23 molecules of hydrogen gas.
We have to know that the number of molecules in one mole of a substance is obtained from the Avogadro's number.
We know that;
1 mole of hydrogen contains 6.02 × 10^23 molecules of hydrogen
0.25 mole of hydrogen contains 0.25 mole × 6.02 × 10^23 molecules/1 mole
= 1.5 * 10^23 molecules
Therefore, 0.25 mole of hydrogen contains 1.5 * 10^23 molecules of hydrogen gas.
Learn more about Avogadro's number: https://brainly.com/question/1445383
