Most-tested fact (appears almost annually): When both nitrogen AND sulfur are present in Lassaigne's test, the color observed with FeCl3 is BLOOD-RED (not Prussian blue). NaSCN forms, giving Fe(SCN)3.

Second most-tested fact: KMnO4/oxalic acid titration is self-indicating — NO external indicator (no phenolphthalein, no methyl orange, no starch). Endpoint = first persistent pink.

Third most-tested fact: Temperature for KMnO4/oxalic acid titration = 60–70 °C. Not room temperature (too slow) and not boiling (oxalic acid decomposes).

Common PYQ pattern — silver halide colors: Questions ask to arrange AgCl, AgBr, AgI in order of color intensity (white → pale yellow → yellow) or NH3 solubility (soluble → partially soluble → insoluble).

Iodoform specificity question type: "Which compound does NOT give iodoform test?" Answer is typically benzaldehyde or 3-pentanone (non-methyl ketone) depending on the options.

Fehling's test trap: "Which aldehyde does NOT reduce Fehling's?" Answer: Benzaldehyde (aromatic aldehyde, resistant to Fehling's).

Carbylamine trap: "Carbylamine test is positive for — primary/secondary/tertiary amine?" Answer: Primary amine ONLY.

KMnO4 stoichiometry questions: "How many moles of oxalic acid react with 0.1 mol KMnO4?" Use the 5:2 ratio (5 mol oxalic acid per 2 mol KMnO4) → 0.25 mol oxalic acid.

Halogen test pretreatment: "Why is HNO3 added before AgNO3 in Lassaigne's halogen test?" Answer: To decompose NaCN (gives AgCN white interference) and Na2S (gives Ag2S black interference) from the extract.