Q4 / 180 · COMEDK 2025 (10 May Shift 1) · Chemistry
Choose the correct statement.
- ACalcium and Magnesium metals are manufactured by electrolysis of aqueous solutions of their salts
- BThe oxo-anion $\mathrm{ClO}_3^{-}$ does not undergo disproportionation reaction
- Correct answerCNitride ion \(\mathrm{N}^{-3}\) cannot act as an oxidising agent
- DIn alkaline medium the reduction of $\mathrm{MnO}_4^{-}$ ion involves gain of 5 electrons
Solution
Calcium and Magnesium are highly reactive metals with standard reduction potentials more negative than that of water. Electrolysis of their aqueous salt solutions results in the evolution of hydrogen gas at the cathode rather than the deposition of the metal. Therefore, they are manufactured by the electrolysis of their molten chloride salts.
The chlorate ion $\mathrm{ClO}_{3}^{-}$ contains chlorine in the $+5$ oxidation state. It can undergo disproportionation into chloride ($-1$) and perchlorate ($+7$) ions, especially in acidic or basic conditions, making the statement that it does not undergo disproportionation incorrect.
The nitride ion $\mathrm{N}^{3-}$ has nitrogen in its lowest possible oxidation state of $-3$. Since it cannot be reduced further, it cannot act as an oxidizing agent. It can only act as a reducing agent by losing electrons to form nitrogen gas or other nitrogen-containing species.
In an alkaline medium, the reduction of the permanganate ion $\mathrm{MnO}_{4}^{-}$ (where Mn is $+7$) typically proceeds to the manganate ion $\mathrm{MnO}_{4}^{2-}$ (where Mn is $+6$), which involves a gain of 1 electron, or to manganese dioxide $\mathrm{MnO}_{2}$ (where Mn is $+4$), which involves a gain of 3 electrons. The gain of 5 electrons occurs in an acidic medium where $\mathrm{MnO}_{4}^{-}$ is reduced to $\mathrm{Mn}^{2+}$.
Answer: Nitride ion \(\mathrm{N}^{-3}\) cannot act as an oxidising agent
The chlorate ion $\mathrm{ClO}_{3}^{-}$ contains chlorine in the $+5$ oxidation state. It can undergo disproportionation into chloride ($-1$) and perchlorate ($+7$) ions, especially in acidic or basic conditions, making the statement that it does not undergo disproportionation incorrect.
The nitride ion $\mathrm{N}^{3-}$ has nitrogen in its lowest possible oxidation state of $-3$. Since it cannot be reduced further, it cannot act as an oxidizing agent. It can only act as a reducing agent by losing electrons to form nitrogen gas or other nitrogen-containing species.
In an alkaline medium, the reduction of the permanganate ion $\mathrm{MnO}_{4}^{-}$ (where Mn is $+7$) typically proceeds to the manganate ion $\mathrm{MnO}_{4}^{2-}$ (where Mn is $+6$), which involves a gain of 1 electron, or to manganese dioxide $\mathrm{MnO}_{2}$ (where Mn is $+4$), which involves a gain of 3 electrons. The gain of 5 electrons occurs in an acidic medium where $\mathrm{MnO}_{4}^{-}$ is reduced to $\mathrm{Mn}^{2+}$.
Answer: Nitride ion \(\mathrm{N}^{-3}\) cannot act as an oxidising agent
Hence, the correct answer is option: 'C'.