Test Index

COMEDK 2025 Morning Solved Paper

Question : 67 of 180

Marks: +1, -0

Choose the correct statement.

Calcium and Magnesium metals are manufactured by electrolysis of aqueous solutions of their salts
The oxo-anion $\mathrm{ClO}_3^{-}$ does not undergo disproportionation reaction
Nitride ion $\mathrm{N}^{-3}$ cannot act as an oxidising agent
In alkaline medium the reduction of $\mathrm{MnO}_4^{-}$ ion involves gain of 5 electrons

Solution:

Concept:

Identify the true statement among four chemistry facts about reduction, oxidation, and electrolysis.

Explanation:

Option A is false.

Calcium and magnesium are extracted by electrolysis of their molten chlorides, not aqueous solutions.

In aqueous solution, water is reduced more easily than these metal ions, producing hydrogen gas instead of the metal.

Option B is false.

The chlorate ion

\mathrm{ClO}_3^-

can undergo disproportionation in acidic medium.

For example:

3\,\mathrm{ClO}_3^- + 3\,\mathrm{H}^+ \longrightarrow 2\,\mathrm{ClO}_2 + \mathrm{ClO}_4^- + \mathrm{H}_2\mathrm{O}

Here chlorine both increases and decreases its oxidation state.

Option D is false.

In alkaline medium, permanganate

\mathrm{MnO}_4^-

is reduced to manganate

\mathrm{MnO}_4^{2-}

This reduction involves only one electron:

\mathrm{MnO}_4^- + e^- \longrightarrow \mathrm{MnO}_4^{2-}

It does not gain five electrons.

Option C is true.

The nitride ion

\mathrm{N}^{3-}

already has a full octet and a high negative charge.

It acts as a strong base and reducing agent.

It cannot accept additional electrons, so it cannot act as an oxidising agent.

Answer:

Option C

Go to Question:

Prev Question

Next Question