Which of the following samples at standard temperature and pressure (STP) contains the same number of atoms as 18 liters of Ne(g) at STP?

• A. 18 liters of Ar(g)
• B. 36 liters of He(g)
• C. 18 liters of N2(g)
• D. 9 liters of O2(g)

Answer: (A)

Verified step by step guidance

1. Recall that at standard temperature and pressure (STP), one mole of any ideal gas occupies 22.4 liters. This means the number of moles of gas can be found by dividing the volume of the gas by 22.4 L/mol: \(\text{moles} = \frac{\text{volume (L)}}{22.4}\).
2. Calculate the number of moles of neon (Ne) in 18 liters at STP using the formula above: \(n_{Ne} = \frac{18}{22.4}\) moles.
3. Determine the total number of atoms in the neon sample. Since neon is a monoatomic gas, the number of atoms equals the number of moles times Avogadro's number, but for comparison, just keep it in moles of atoms: \(n_{atoms, Ne} = n_{Ne}\).
4. For each of the other gases, calculate the number of moles using their given volumes and the same formula. Then, find the total number of atoms in each sample. Remember that diatomic gases like \(N_2\) and \(O_2\) have 2 atoms per molecule, so multiply the moles of molecules by 2 to get moles of atoms.
5. Compare the moles of atoms in each sample to the moles of atoms in the 18 L Ne sample. The sample with the same number of atoms will have the same total moles of atoms as the neon sample.