Final answer:
The molecules in a liquid are much closer together than those in a gas. While the average kinetic energy at the same temperature is similar for both phases, liquid molecules face more intermolecular forces and thus move less freely compared to gas molecules.
Step-by-step explanation:
The relationship between molecules in a liquid and those in a gas at the same temperature can be described by comparing the distance between molecules and their kinetic energy. In a gas, molecules are much farther apart than in a liquid. This is because the forces between gas molecules can often be ignored, except during collisions, since they have large separations compared to their sizes. In contrast, molecules in a liquid are very close together, with no empty space between them, leading to higher density and lower compressibility than gases.
Concerning kinetic energy, molecules in both liquids and gases possess kinetic energy that depends on the temperature, meaning that at the same temperature, the average kinetic energy of the molecules is the same. However, in a liquid, the kinetic energy must be high enough to overcome the intermolecular attractive forces that are much more significant than in gases. So, while individual gas molecules may move faster due to fewer collisions and less resistance, the average kinetic energy is comparable in both phases at the same temperature.
Therefore, the best description of the relationship is A) Molecules in the liquid are much closer together than those in the gas. This is because the molecular kinetic energy of substances in the same phase depends on temperature, and since our comparison assumes the same temperature for both phases, the kinetic energy should be similar. Thus, option B is incorrect, and C is also incorrect due to the same reason. Given this, the correct answer would be D) Both a and b are correct.