Which statement is true about 0.25 mole of O_2 and 0.25 mole of NH_3?

• A. 0.25 mole of O_2 contains more molecules than 0.25 mole of NH_3.
• B. Both samples contain the same number of molecules.
• C. 0.25 mole of NH_3 contains more molecules than 0.25 mole of O_2.
• D. Both samples have the same mass.

Answer: (B)

Verified step by step guidance

1. Recall that a mole is a unit that represents a fixed number of particles, specifically Avogadro's number, which is approximately \$6.022 \times 10^{23}$ particles per mole.
2. Understand that 0.25 mole of any substance contains the same number of molecules, because the mole counts the number of entities regardless of the type of molecule.
3. Compare the number of molecules in 0.25 mole of \(O_2\) and 0.25 mole of \(NH_3\): both have \$0.25 \times 6.022 \times 10^{23}$ molecules, so the number of molecules is the same.
4. Consider the mass of each sample: since the molar masses of \(O_2\) and \(NH_3\) are different, the masses of 0.25 mole of each will not be the same.
5. Conclude that the true statement is that both samples contain the same number of molecules, but they do not have the same mass.