Pattern 1: Lassaigne's Test N + S Trap (Appears almost every alternate year)

PYQ Core Concept: When N and S are both present → NaSCN forms → FeCl3 gives BLOOD-RED, not Prussian blue.

Sample question type: "The compound thiourea (H2N-CS-NH2) on Lassaigne's test gives __ color with FeCl3." Answer: Blood-red (because both N and S are present → NaSCN forms)

Frequency: Very high — direct recall. Appears as straightforward MCQ and as the "trap" option in complex compound identification.

Pattern 2: KMnO4/Oxalic Acid — Self-Indicating + Temperature

PYQ Core Concept: NO indicator needed; temperature = 60–70 °C; Mn changes +7 → +2.

Sample question type: "In the titration of oxalic acid with KMnO4, which indicator is used?" Answer: No indicator (self-indicating)

Frequency: High. Often combined with: "what is the temperature?" or "what is the role of H2SO4?"

Pattern 3: Silver Halide Differentiation

PYQ Core Concept: AgCl white/soluble in NH3; AgBr pale yellow/partially soluble; AgI yellow/insoluble.

Sample question type: "Arrange in order of decreasing solubility in NH3: AgCl, AgBr, AgI" Answer: AgCl > AgBr > AgI

Frequency: Moderate-high. Appears as ranking questions or identification questions.

Pattern 4: Iodoform Test Specificity

PYQ Core Concept: Iodoform positive = methyl ketones, CH3CHO, C2H5OH, and CH3CHOH-R (secondary alcohols oxidizable to methyl ketones).

Sample question type: "Which does NOT give iodoform test: acetaldehyde / acetone / benzaldehyde / ethanol?" Answer: Benzaldehyde

Frequency: Moderate. Watch for: 3-pentanone (NEGATIVE), isopropanol (POSITIVE).

Prediction for NEET 2026

Based on recent 3-year trends: Lassaigne's N+S trap, AgNO3 halogen test conditions (why HNO3), and iodoform specificity are likely to appear. One mechanism-based question on preparation of acetanilide or p-nitroacetanilide is also probable.