Question

The oxidation states of $Cr$ in $ [Cr(H_2O)_6]Cl_3, [Cr(C_6H_6)_2]$, and $K_2[Cr(CN)_2(O)_2(O_2)(NH_3)]$ respectively are :

• A. +3, +4, and +6
• B. +3, +2, and +4
• C. +3, 0, and +6
• D. +3, 0, and +4

Answer 1

The Correct Option is C

To determine the oxidation states of chromium (\(Cr\)) in the given complexes, let's analyze each complex individually: 

1. \([Cr(H_2O)_6]Cl_3\):
   • The complex is a hexaaqua complex where water \((H_2O)\) is a neutral ligand (oxidation state = 0).
   • Each chloride ion \((Cl^-)\) contributes -1 to the charge.
   • Since there are three chloride ions, the collective charge from chlorides is -3.
   • To balance this charge, the oxidation state of \(Cr\) must be +3.
   • Therefore, the oxidation state of chromium in this compound is +3.
2. \([Cr(C_6H_6)_2]\):
   • This complex is a bis-benzene chromium complex, where benzene \((C_6H_6)\) is neutral (oxidation state = 0).
   • Since there are no anions or cations apart from the ligand, the oxidation state of \(Cr\) must also be 0 to maintain the compound's neutrality.
   • Therefore, the oxidation state of chromium in this complex is 0.
3. \(K_2[Cr(CN)_2(O)_2(O_2)(NH_3)]\):
   • Potassium ions \((K^+)\) contribute a total of +2 charge.
   • Cyanide \((CN^-)\) and oxide ions \((O^{2-})\) are ligands with charges of -1 and -2 respectively.
   • The dioxygen ligand \((O_2)\) is neutral (acting as a bracket bridge). Similarly, ammonia \((NH_3)\) is also neutral.
   • Knowing that potassium gives a total positive charge:
     • Total charge of ligands: -2 (from two \(CN^-\span>) and -4 (from two\)
   • Thus, to balance the charges: \(x + (-2) + (-4) = -2\) where \(x\) is the oxidation state of \(Cr\).
   • Solving gives \(x = +6\).
   • Hence, the oxidation state of chromium in this compound is +6.

In conclusion, the oxidation states of \(Cr\) in the given complexes are +3, 0, and +6, respectively.