Appeared in: 2026 (3 sets)
According to Werner's theory, the primary valencies of the central metal atom :
(A) are satisfied by neutral molecules or negative ions.
(B) are equal to its coordination number.
(C) are satisfied by negative ions.
(D) are non-ionisable.
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Official Evaluation Steps & EL10 Insight
Question: According to Werner's theory, the primary valencies of the central metal atom:
Step 1 (Governing Principle of Werner's Theory): [0.5 Mark]
According to Alfred Werner's postulates for coordination compounds:
- Primary Valency: Corresponds to the oxidation state of the central metal ion. These are ionisable and are always satisfied by negative ions (anions).
- Secondary Valency: Corresponds to the coordination number. These are non-ionisable and are satisfied by neutral molecules or negative ions (ligands).
Step 2 (Analysis of Options): [0.25 Mark]
- (A) Incorrect: Neutral molecules satisfy secondary valencies.
- (B) Incorrect: Coordination number corresponds to secondary valency.
- (C) Correct: Primary valencies are satisfied by negative ions to balance the positive charge of the metal.
- (D) Incorrect: Primary valencies are ionisable (they dissociate in solution).
Step 3 (Final Concluded Answer): [0.25 Mark]
The correct option is (C).
💡 EL10 Concept Insight: Think of the primary valency as the "debt" (oxidation state) the metal atom needs to pay off using negative charges (like $Cl^-$), while the secondary valency is the "entourage" of molecules surrounding the metal to form the complex shape.