The question requires matching concepts from LIST-I with their corresponding descriptions in LIST-II.

Matching Concepts from LIST-I and LIST-II

We analyze each item from LIST-I:

• A. Gilliland correlation: This correlation is used in chemical engineering, particularly in distillation design. It provides a relationship between the operating reflux ratio, the number of separation stages, minimum reflux ratio, and minimum stages. Therefore, it matches with IV. Reflux Ratio and stages relation.
• B. Relative volatility ($\alpha$): Relative volatility is a fundamental property that indicates how easily two components can be separated using distillation. A higher value signifies easier separation. Thus, it corresponds to III. Separation ease.
• C. Steady state diffusion: In diffusion processes operating under steady-state conditions, the concentration or flux at any point remains constant over time. This implies there is I. With time no accumulation.
• D. Number of transfer unit (NTU): NTU is a dimensionless measure used in process design (like heat exchangers and mass transfer equipment) to quantify the effectiveness of a transfer process. It relates to the required size or effort for separation, hence indicating the II. Difficulty in separation measurement or performance evaluation.

Correct Matching

Based on the analysis, the correct matching is:

• A - IV
• B - III
• C - I
• D - II

This corresponds to the option A-IV, B-III, C-I, D-II.