Read the passage carefully and answer the questions.
Sodium dichromate \( Na_2Cr_2O_7 \) and Potassium dichromate \( K_2Cr_2O_7 \), are strong oxidizing agents; in acidic solution, its oxidising action can be represented as follows:
\( Cr_2{O_7}^{2-}+ 14H^++ 6e^-→2Cr^{3+}+ 7H_2O \) \( (E° = 1.33V) \)
The chromates and dichromates are interconvertible in aqueous solution depending upon pH of the solution. The chromate ion is tetrahedral whereas the dichromate ion consists of two tetrahedra sharing one corner with Cr-O-Cr bond angle of 126°
Potassium permanganate is prepared by fusion of \( MnO_2 \) with an alkali metal hydroxide and an oxidising agent like \( KNO_3 \). This produces the dark green \( K_2MnO_4 \) which disproportionates in a neutral or acidic solution to give permanganate. It is a strong oxidizing agent. Hydrogen ion concentration of the solution plays an important part in the reduction of permanganate to manganate, manganese dioxide and manganese(II) salt.
Potassium permanganate forms dark purple (almost black) crystals which are isostructural with those of \( KClO_4 \). The salt is not very soluble in water (6.4 g/100 g of water at 293 K), but when heated it decomposes at 513 K.
Potassium dichromate is used in the leather industry because of its nature as
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Oxidant
In potassium dichromate, chromium is in its highest oxidation state, +6. Dichromate can therefore only take up electrons: it is a strong oxidising agent, and in acidic solution each \( \ce{Cr2O7^2-} \) ion gains 6 electrons and is reduced to \( \ce{Cr^3+} \):
\( \displaystyle \ce{Cr2O7^2- + 14H^+ + 6e^- -> 2Cr^3+ + 7H2O}\quad (E^\circ = 1.33\ \mathrm{V}) \)
This oxidising nature is what the question asks about: potassium dichromate is used in the leather industry and as an oxidant for preparing many azo compounds.
Why the other options are incorrect
Option (2) Reductant — Incorrect. A reductant gives out electrons and is itself oxidised. Chromium in dichromate is already at +6, the group oxidation state, so it cannot be oxidised further.
Option (3) Alkali media — Incorrect. Potassium dichromate is a salt, not a base. In fact, in alkaline solution dichromate changes to chromate, \( \ce{Cr2O7^2- + 2OH^- -> 2CrO4^2- + H2O} \).
Option (4) disproportionating media — Incorrect. Disproportionation is the simultaneous oxidation and reduction of one species. In the passage it is manganate, \( \ce{K2MnO4} \), that disproportionates in neutral or acidic solution; dichromate does not.
NCERT (2026-27 edition):
Potassium Dichromate K2Cr2O7 – “Potassium dichromate is a very important chemical used in leather industry and as an oxidant for preparation of many azo compounds.”