Final answer:
The attraction between molecules leads to a decrease in pressure at intermediate P and low T because the molecules move closer together resulting in less forceful and less frequent collisions with the container walls.
Step-by-step explanation:
The question asks how the attraction between molecules affects pressure observed at intermediate pressures (P) and low temperatures (T). The attraction between molecules, or intermolecular forces, tends to pull gas molecules closer together. At low temperatures molecules have lower kinetic energy (KE) compared to these attractive forces, resulting in fewer effective collisions with the walls of the container after they interact with each other. Therefore, decreases pressure would be the correct answer for the behavior of gases under these conditions as compared to what would be predicted by the ideal gas law.
This decrease in pressure is due to a reduced frequency and force of collisions against the container walls due to these attractive forces. This effect becomes more evident as the gas is compressed (higher pressures) and the temperature is lowered emphasizing the non-ideal behavior of real gases.