Step 1: Population → Density.
Population is commonly measured and studied in terms of density, which shows the number of people living per unit area. Hence, A is correctly matched with IV.
Step 2: Communication → Immobility.
Better communication reduces the need for physical movement, leading to relative immobility of people and activities. Therefore, B matches with III.
Step 3: Agriculture → Productivity.
Agriculture is directly related to productivity, as it depends on crop yield and output per unit of land. Thus, C is matched with I.
Step 4: Industrial → Demand.
Industrial development is closely linked with demand for goods and services in the economy. Hence, D corresponds to II.
Step 5: Conclusion.
The correct matching is A–IV, B–III, C–I, D–II, which corresponds to option (B).