At standard temperature and pressure (STP), which of the following samples of matter has the greatest average distance between its molecules?

• A. Liquid water (H_2O)
• B. Solid carbon dioxide (CO_2)
• C. Oxygen gas (O_2)
• D. Solid sodium chloride (NaCl)

Answer: (C)

Verified step by step guidance

1. Understand that the average distance between molecules depends on the state of matter: solids have molecules closely packed, liquids have molecules less tightly packed, and gases have molecules far apart.
2. Recall that at standard temperature and pressure (STP), gases occupy much more volume than solids or liquids, meaning their molecules are much farther apart on average.
3. Identify the states of each sample: liquid water is a liquid, solid carbon dioxide and solid sodium chloride are solids, and oxygen gas is a gas at STP.
4. Since gases have the greatest average distance between molecules compared to solids and liquids, oxygen gas (O_2) will have the largest average intermolecular distance.
5. Therefore, the sample with the greatest average distance between its molecules at STP is the oxygen gas (O_2).