Error 1: Assuming $F^{-}$ is a strong field ligand

• Wrong logic: "Fluorine is the most electronegative, so $F^{-}$ must cause the most splitting."
• Correct: $F^{-}$ is a weak field ligand. Field strength in spectrochemical series depends on σ-donation and π-back-bonding ability, NOT electronegativity. $F^{-}$ is a strong π-donor that reduces effective $\Delta o$.

Error 2: Confusing octahedral and tetrahedral d-orbital labels

• Wrong: t_{2}g is always the lower set.
• Correct: t_{2}g is lower only in octahedral. In tetrahedral, the e set is lower and t_{2} is higher — the order is completely inverted.

Error 3: Applying $\Delta t$ = $\Delta o$

• Wrong: Using $\Delta o$ directly for tetrahedral.
• Correct: $\Delta_t = \frac{4}{9}\Delta_o$. Tetrahedral splitting is always smaller.

Error 4: Wrong KMnO4 product in basic medium

• Wrong: Writing $MnO_{2}$ (brown) in basic medium.
• Correct: $MnO_{4}^{2-}$ (manganate, green) in basic medium. $MnO_{2}$ is the neutral medium product.

Error 5: Confusing primary and secondary valence (Werner's theory)

• Wrong: Thinking coordination number (secondary valence) is ionisable.
• Correct: Primary valence = oxidation state = ionisable. Secondary valence = coordination number = non-ionisable, directional, and satisfies the geometry.

Error 6: Naming ligands in wrong order

• Wrong: Listing ligands in order of denticity or by the metal's preference.
• Correct: IUPAC requires alphabetical order of ligand names, ignoring multiplying prefixes (di-, tri-, bis-).

Error 7: Forgetting that all actinoids are radioactive, not all lanthanoids

• Wrong: "All f-block elements are radioactive."
• Correct: Lanthanoids are mostly non-radioactive (except Pm). All actinoids are radioactive.

Error 8: Confusing linkage isomers and ionisation isomers

• Wrong: Treating any two complexes with the same formula as the same type of isomer.
• Correct: Linkage isomerism occurs when an ambidentate ligand ($NO_{2}^{-}$, S$CN^{-}$) changes its donor atom. Ionisation isomerism occurs when a ligand and a counter-ion exchange positions (one moves inside the coordination sphere, the other moves out).