Question

The oxidising power of $[CrO_{4}]^{2-}, [MnO_{4}]^{2-}$ and $[FeO_{4}]^{2-}$ follows the order

• A. $[CrO_{4}]^{2-}<\, [MnO_{4}]^{2-}<\, [FeO_{4}]^{2-}$
• B. $[FeO_{4}]^{2-}<\, [MnO_{4}]^{2-}<\, [CrO_{4}]^{2-}$
• C. $[MnO_{4}]^{2-}<\,[FeO_{4}]^{2-}<\, [CrO_{4}]^{2-}$
• D. $[CrO_{4}]^{2-}<\, [FeO_{4}]^{2-}<\,[MnO_{4}]^{2-}$

Answer 1

Answer: (A)

All have $+6$ oxidation state but due to smaller size on going from $Cr$ to $Fe$, charge density increases from $Cr$ to $Fe$ and hence tendency to accept $e^{-}$ increases
$\therefore $ oxidising power $[CrO_{4}]^{2-}<\, [MnO_{4}]^{2-}<\,[FeO_{4}]^{2-}$