Question

Gases deviate from ideal gas behaviour because of their molecules:
  (A) possess negligible volume
  (B) have forces of attraction between them
  (C) are polyatomic
  (D) are not attracted to one another

Answer 1

Hint: Ideal gases are those gases which obey kinetic molecular theory of gases. In the ideal behaviour of gases, the volume occupied by gas molecules and forces of attraction between molecules is not taken into account. Real gases deviate from the behaviour of ideal gases since the real gas molecules do not satisfy mainly these two conditions of ideal gases.

Complete step by step solution:
-Let's start with the kinetic theory of gases. The theory was introduced in order to explain the behaviour of gases. The gas molecules were assumed as spheres in this theory and there were mainly two assumptions related to the kinetic theory of gases. The two main assumptions are given below
(i) When compared to the total volume occupied by the gas, the volume occupied by the gas molecules is negligibly small.
(ii) It is considered that there is no force of attraction between gas molecules and hence the collision between molecules are treated as elastic.
-Let's analyze each of these assumptions. Only at a higher temperature and lower pressure, the volume occupied by the gas molecules is negligible when compared to the total volume of gas. At lower temperatures and higher pressures, the molecules become compressed and the volume of gas molecules become significant Thus, the first assumption holds only at specific conditions.
-Similarly, in the second assumption, at low temperature or high pressure, the total volume of the gas becomes reduced and force of attraction between molecules becomes significant and the attraction between molecules cannot be neglected.
-As we mentioned above, the real gases deviate from the ideal gas behaviour because of the force of attraction between molecules.

Therefore, the answer is option (B).

Note: It should be noted that the completely ideal gas behaviour is a hypothetical concept. In ideal behaviour of gases, the gas molecules do not have any interaction and do not occupy space, as assumed in the kinetic theory of gases. But in reality, this is not possible as we get errors by applying the ideal gas law and hence van der Waals corrected the ideal gas behaviour by introducing suitable constants.