The oxidation state of Cobalt in diamagnetic octahedral complex [Co(NH3)6]3+ is:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → +3
The oxidation state of the central metal is found from the charge balance: the charge of the complex equals the oxidation state of the metal plus the charges of the ligands. \( \ce{NH3} \) is a neutral ligand:
\( \displaystyle x + 6(0) = +3 \;\Rightarrow\; x = +3 \)
This fits the complex being diamagnetic: Co (Z = 27) [Ar]3d74s2 → \( \ce{Co^{3+}} \) 3d6. \( \ce{NH3} \) causes the six d electrons to pair up in the t2g level (t2g6eg0), leaving no unpaired electron.