Question

Which of the following statements is incorrect?

• A. Co³⁺ and Fe²⁺ have same number of unpaired electrons.
• B. Of all the known elements, Silver has the highest electrical conductivity at room temperature.
• C. To form a substitute alloy, the difference between the atomic radii of solvent and solute atoms should be less than 15%.
• D. If the standard electrode potential (E^) of a metal is large and negative, the metal is a powerful oxidising agent.

Hint:

To remember redox strength: - More Negative E^: Stronger Reducing Agent (Best at losing electrons). - More Positive E^: Stronger Oxidising Agent (Best at gaining electrons).

Answer 1

The Correct Option is D

Concept: This question tests fundamental principles across coordination chemistry, metallurgy, and electrochemistry. Key concepts: • Electronic Configuration: Determining unpaired electrons in transition metal ions. • Hume-Rothery Rules: Criteria for solid solubility and alloy formation. • Electrochemical Series: Relationship between E^ and redox strength.
Iron (Fe, Z=26) configuration: [Ar] 3d⁶ 4s². Fe²⁺: [Ar] 3d⁶. Unpaired e^- = 4.
Cobalt (Co, Z=27) configuration: [Ar] 3d⁷ 4s². Co³⁺: [Ar] 3d⁶. Unpaired e^- = 4.
Both have 4 unpaired electrons. Statement is correct.
(b) Silver is indeed the most conductive element. Statement is correct.
(c) According to Hume-Rothery rules, for a substitutional solid solution (alloy), the atomic radii difference must be within ±15%. Statement is correct.
A large negative E^ means the metal has a strong tendency to lose electrons (undergo oxidation). This makes the metal a powerful reducing agent, not an oxidising agent. Oxidising agents are themselves reduced and typically have positive E^ values. Therefore, statement (d) is incorrect.