Error 1 — Phosphorus Oxoacid Basicity: Students count total hydrogen atoms in $H_{3}PO_{2}$ or $H_{3}PO_{3}$ and assign basicity = 3. The correct rule is basicity = P-OH bonds only. $H_{3}PO_{2}$ has 1 P-OH (monobasic); $H_{3}PO_{3}$ has 2 P-OH (dibasic). P-H bonds never ionize.

Error 2 — Boric Acid Mechanism: Classifying $H_{3}BO_{3}$ as a Bronsted acid that "donates $H^{+}$." $H_{3}BO_{3}$ is a Lewis acid — it accepts $OH^{-}$ from water. The $H^{+}$ in solution originates from water, not from $H_{3}BO_{3}$.

Error 3 — Catalyst Confusion (Haber vs Ostwald): Using Pt/Rh for Haber or Fe for Ostwald. Haber = Fe at 450°C; Ostwald Step 1 = Pt/Rh at 500°C. Step 2 of Ostwald requires NO catalyst.

Error 4 — Diborane Bond Type: Calling the bridging bonds in $B_{2}H_{6}$ "3c-4e bonds." They are 3c-2e (electron-deficient). 3c-4e bonds exist in other systems (e.g., $PCl_{5}$ axial bonds in some models) but NOT in diborane.

Error 5 — Nitrogen Oxide Classification: Classifying $NO_{2}$ or $N_{2}O_{3}$ as neutral oxides. Only $N_{2}O$ (+1) and NO (+2) are neutral. All nitrogen oxides from $N_{2}O_{3}$ upward are acidic.

Error 6 — Phosphorus Allotrope Stability: Assuming white phosphorus (common lab form) is most stable. Black phosphorus is most thermodynamically stable; white P is least stable and stored under water to prevent spontaneous ignition.

Error 7 — Le Chatelier and Haber Temperature: Stating that "higher temperature gives more $NH_{3}$ in Haber." Higher temperature shifts the exothermic equilibrium backward — less $NH_{3}$. The 450°C compromise sacrifices yield to achieve an acceptable rate.

Error 8 — $NCl_{5}$ Existence: Assuming $NCl_{5}$ exists like $PCl_{5}$. N has no d-orbitals (n=2), so it cannot form more than 4 bonds. $PCl_{5}$ exists because P (n=3) has accessible 3d orbitals.