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Systematic approach for JEE colligative property numericals: Step 1: Identify the property (delta_Tb, delta_Tf, pi, or RLVP). Step 2: Check if solute is electrolyte (find i) or non-electrolyte (i=1). Step 3: Use the correct formula with proper units. Molality for delta_Tb and delta_Tf; molarity for pi; mole fraction for RLVP. Step 4: For molar mass problems, rearrange: M = Kfw21000/(delta_Tfw1) or M = wRT/(piV). Common traps and checks: (a) Always include i for electrolytes — the most common source of errors. (b) Convert temperature to Kelvin for pi = iMRT. (c) R = 0.0821 L.atm/(mol.K) — check units match. (d) For association, remember i < 1 and M_observed > M_actual. (e) delta_Tf is a positive number — the freezing point drops by this amount. (f) With multiple solutes: sum the individual contributions. (g) Alpha values may need to be calculated from the data using i = 1 + (n-1)*alpha. Quick estimates: for 0.1 m non-electrolyte in water, delta_Tf ≈ 0.186 K and delta_Tb ≈ 0.051 K. This helps verify if your calculated answer is in the right ballpark.