A transition metal in its highest oxidation state is expected to behave as
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → An oxidising agent
An oxidising agent takes electrons from another species and is itself reduced.
A metal in its highest oxidation state cannot lose any more electrons; it can only gain electrons and move to a lower state, so it is expected to act as an oxidising agent.
Chromium in dichromate is in its highest state, +6 (the group number). In acid it gains electrons and is reduced to \( \ce{Cr^3+} \).
Why the other options are incorrect
Option (1) Both an oxidising agent and a reducing agent — Incorrect. Acting both ways needs an intermediate oxidation state, which can either gain or lose electrons; the highest state can only gain them.
Option (2) Neither an oxidising agent nor a reducing agent — Incorrect. The metal in its highest state can still gain electrons, so it does take part in redox reactions, as an oxidising agent.
Option (4) A reducing agent — Incorrect. A reducing agent must lose electrons, which a metal in its highest state cannot do; reducing agents such as \( \ce{Cr^2+} \) are metals in a low oxidation state.
NCERT (2026-27 edition):
4.4.1 Oxides and Oxoanions of Metals – “… Sodium and potassium dichromates are strong oxidising agents; the sodium salt has a greater solubility in water and is extensively used as an oxidising agent in organic chemistry. … In acidic solution, its oxidising action can be represented as follows:
\( \displaystyle \ce{Cr2O7^2- + 14H+ + 6e- -> 2Cr^3+ + 7H2O} \quad (E^\circ = 1.33\,\mathrm{V}) \)”