Identify the reactions in which dichromate acts as an oxidising reagent .
`I . Cr_(2)O_(7)^(2)+6Fe^(2+)+14H^(+)rarr 2Cr^(3+) +6Fe^(3+)+7H_(2)O`
`II. Cr_(2)O_(7)^(2-)+2OH^(-1) rarr2CrO_(4)^(2-)+H_(2)O`
`III. Cr_(2)O_(7)^(2-)+6I+14H^(+)rarr 2Cr^(3+)+3I_(2)+7H_(2)O`
`IV. Na_(2)Cr_(2)O_(7)+2KCI rarr K_(2)Cr_(2)O_(7)+2NaCI`

Options

A. I,IV
B. I,III
C. II,III
D. II,IV

Answer

B

Explanation

In reaction I and III dichromate acts as an oxidising reagent .
`Cr_(2)O_(7)^(2-)+6Fe^(2+)+14H^(+)rarr 2Cr^(3+)+6Fe^(3+)+7H_(2)O`
`(II) Cr_(2)O_(7)^(2-)+2OH^(-)rarr2CrO_(7)^(2-)+H_(2)O`
In the above reaction there is no change occuring in the oxidation state of Cr.
(III) `Cr_(2)O_(7)^(2-) + 6I^(-)+14H^(+) rarr 2Cr^(3+) + 3I_(2)+7H_(2)O`
In the above above reaction `Cr^(6+)` has reduced to `Cr^(3+)` and I has oxidised to `I_(2)`.
(IV) `Na_(2)Cr_(2)O_(7)+ 2KCIrarr K_(2)Cr_(2)O_(7)+2NaCI`
In the above reaction no change in the oxidation state of Cr has taken place.