Most Frequently Tested Topics (NEET 2015–2024 Analysis)

Topic 1 — Phosphorus Oxoacid Basicity (High Frequency): The basicity rule (P-OH bonds only) is tested 3–4 times per 5 years. Questions always include a trap option stating "tribasic because 3 H atoms." Master the three structures: $H_{3}PO_{2}$ (1 P-OH, monobasic), $H_{3}PO_{3}$ (2 P-OH, dibasic), $H_{3}PO_{4}$ (3 P-OH, tribasic). The P-H bond is non-ionizable — this is the single most important sentence in this chapter.

Topic 2 — Haber Process Conditions: Questions test Fe catalyst (not Pt), 450°C temperature (not 500°C), and 200 atm pressure. They also test Le Chatelier reasoning: why is 450°C a compromise (rate vs yield)? Why does high pressure improve yield (4 mol gas → 2 mol gas)? NEET frequently provides false options stating Pt catalyst or 300°C temperature.

Topic 3 — Ostwald Process (Multi-step): PYQs test: (a) catalyst for each step (Pt-Rh for Step 1 only, none for Steps 2 and 3), (b) temperature of Step 1 (500°C, not 450°C), (c) the product and stoichiometry of Step 3, and (d) the fact that NO from Step 3 is recycled. Confusion with $V_{2}O_{5}$ (Contact Process catalyst) appearing in wrong-answer options is common.

Topic 4 — Nitrogen Oxide Properties: Matching oxidation states, paramagnetic character, and anhydride identity to the correct nitrogen oxide. Key facts tested: $N_{2}O$ and NO are neutral; only NO and $NO_{2}$ are paramagnetic; $N_{2}O${3} → H$NO_{2}$; $N_{2}O${5} → $HNO_{3}$.

Topic 5 — Boric Acid Lewis Acid Nature: "Why is $H_{3}BO_{3}$ acidic?" — always tests Lewis vs Bronsted distinction. Wrong options describe $H_{3}BO_{3}$ donating $H^{+}$ like a Bronsted acid. Correct answer: it accepts $OH^{-}$ from water because B is electron-deficient.

Topic 6 — Diborane Bonding: 3c-2e (not 3c-4e) bonds in $B_{2}H_{6}$; 2 bridging H (not 4); no B-B bond present.