Identify the reactions in which dichromate acts as an oxidising reagent. I. Cr ₂ O ₇²⁻+6 Fe ²⁺+14 H ⁺ 2 Cr ³⁺+6 Fe ³⁺+7 H ₂ O II. Cr ₂ O ₇²⁻+2 OH ⁻ 2 CrO ₄²⁻+ H ₂ O III. Cr ₂ O ₇²⁻+6 I ⁻+14 H ⁺ 2 Cr ³⁺+3 I ₂+7 H ₂ O IV. Na ₂ Cr ₂ O ₇+2 KCl K ₂ Cr ₂ O ₇+2 NaCl

Step-by-step solution

In reaction I and III, dichromate acts as an oxidising reagent. (I) Cr ₂ O ₇²⁻+6 Fe ²⁺+14 H ⁺ 2 Cr ³⁺+6 Fe ³⁺+7 H ₂ O In the above reaction, Cr ⁶⁺ reduced to Cr ³⁺ and Fe ²⁺ oxidised to Fe ³⁺ . (II) Cr ₂ O ₇²⁻+2 OH ⁻ 2 CrO ₄²⁻+ H ₂ O In the above reaction, there is no change occuring in the oxidation state of Cr . (III) Cr ₂ O ₇²⁻+6 I ⁻+14 H ⁺ 2 Cr ³⁺ +3 I ₂+7 H ₂ O In the above reaction, Cr ⁶⁺ has reduced to Cr ³⁺ and I ⁻ has oxidised to I ₂ . (IV) Na ₂ Cr ₂ O ₇+2 KCl K ₂ Cr ₂ O ₇+2 NaCl In the above reaction, no