Most Tested (NEET 2016–2024)

1. Molar mass calculation from $\Delta Tb$ or $\Delta Tf$ (High frequency — nearly every year) Formula: $M_{2}$ = Kb × w_{2} × 1000 / ($\Delta Tb$ × w_{1}). Ensure w_{1} is in grams (the ×1000 factor converts to kg). For electrolytes, use i in $\Delta Tb$ = iKbm but remember the molar mass formula already accounts for i if observed $\Delta Tb$ is given directly.

2. Van't Hoff factor — degree of dissociation/association i = $\Delta Tf$(obs) / $\Delta Tf$(expected). Then α = (i − 1)/(n − 1) for dissociation; α = 2(1 − i) for dimerization. Acetic acid + benzene dimerization questions appear 1–2 times per 5-year cycle.

3. Comparing colligative properties for different solutes "Which has highest boiling point at same molality?" → highest i wins → $AlCl_{3}$ (i=4) > $CaCl_{2}$ (i=3) > NaCl (i=2) > glucose (i=1). These questions have appeared every alternate year.

4. Ideal vs non-ideal solution identification Pair identification: Benzene + toluene (ideal), Ethanol + water (positive, min boiling), $CHCl_{3}$ + acetone (negative, max boiling). The $\Delta H$_mix and $\Delta V$_mix signs are frequently tested as assertion-reason questions.

5. Osmotic pressure numericals π = iCRT with T in Kelvin. For polymer/protein molar mass: M = wRT/(πV). The contrast that "osmometry is preferred for macromolecules because other colligative effects are too small to measure" is a reasoning-type NEET staple.

6. Henry's Law applications "Bends" and carbonation questions. K_H increases with temperature = solubility decreases. Often tested as assertion-reason or one-liner MCQ.

7. Positive/negative deviation — $\Delta H$ and $\Delta V$ signs Negative deviation: $\Delta H$_mix < 0 (exothermic), $\Delta V$_mix < 0 (contraction). This is frequently tested as a fill-in or MCQ on thermodynamic signatures.