Deviation from Ideal Gas Behaviour — Predicted 2026

AI-Predicted Question Angles for UPSC 2026

Based on trend analysis, current affairs, and recurring themes in Deviation from Ideal Gas Behaviour.

Comparative analysis of 'a' and 'b' for different gases.

high

NEET often tests the application of concepts rather than rote memorization. Comparing 'a' values to predict ease of liquefaction or 'b' values to infer molecular size for a given set of gases is a classic application-based question. For example, ranking $NH_3, H_2O, CH_4$ based on their 'a' values (due to hydrogen bonding in $NH_3, H_2O$) or 'b' values (based on molecular size) is a likely scenario. This tests both conceptual understanding and analytical skills.

Graphical interpretation of Z vs. P at different temperatures.

medium

While Z vs. P at a single temperature is common, questions might evolve to show multiple curves for the same gas at different temperatures. Aspirants would need to identify the Boyle temperature curve (where Z is close to 1 for a range) or explain how increasing/decreasing temperature affects the shape of the Z curve, particularly the depth of the dip below Z=1. This requires a deeper understanding of how temperature influences the dominance of attractive vs. repulsive forces.

Conceptual questions linking critical constants to van der Waals constants.

low

Direct numerical problems involving critical constants ($T_c, P_c, V_c$) are less likely, but conceptual questions linking their definitions to the van der Waals constants 'a' and 'b' could appear. For instance, asking which constant ('a' or 'b') primarily influences the critical temperature or critical pressure, or a qualitative comparison of $T_c$ for two gases based on their 'a' and 'b' values. This tests the understanding of the relationships $T_c = \frac{8a}{27Rb}$, $P_c = \frac{a}{27b^2}$, and $V_c = 3b$ without requiring complex calculations.