QJEEM18Ch0ac7: JEE Main 2018 Chemistry - Class 12 JEEM18Ch0ac7 Solution: The oxidation states of Cr in [Cr(H 2 O) 6 ]Cl 3 , [Cr(C 6 H 6…

Assume oxidation state of Cr in all the compounds = x

(i) $\,\,\,$ In [Cr(H₂O)₆] Cl₃ oxidation state of Cr is

x + 0 $\times$ 6 + ( $-$ 1 $\times$ ) = O

$\Rightarrow \,\,\,\,\,$ x + 0 $-$ 3 = O

$\Rightarrow \,\,\,\,$ x = + 3

(ii) $\,\,\,$ [Cr (C₆ H₆)₂] oxidation state of Cr is

x + 0 $\times$ 2 = 0

$\Rightarrow \,\,\,\,$ x = 0

(iii) $\,\,\,$ In K₂ [ Cr(CN)₂ (O)₂ (O₂) (NH₃)] oxidation state of Cr is

1 $\times$ 2 + x + ( $-$ 1 $\times$ 2) + ( $-$ 2 $\times$ 2) + ( $-$ 2) + 0 = 0

$\Rightarrow \,\,\,\,$ x = + 6

$\therefore\,\,\,$ + 3, 0 and + 6 is the correct answer.

Note :

O₂ molecule can have 0, $-$ 1, $-$ 2 oxidation state but in K₂ [ Cr (CN)₂ (O)₂ (O₂) NH₃ ] if we choose zero as the oxidation state of O₂ then for Cr oxidation state will be $+$ 4. But + 4 oxidation state of Cr is unstable and $+$ 6 is most stable that is why we choose $-$ 2 oxidation state of O₂.