Appeared in: 2026 (3 sets)
According to Alfred Werner, the secondary valence(s) of the central metal atom/ion in a complex :
(A) are non-ionisable
(B) are ionisable
(C) are satisfied by neutral molecules or negative ions
(D) is equal to the coordination number and is normally fixed for a metal
Identify the incorrect statement from the above given statements.
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Official Evaluation Steps & EL10 Insight
Question Analysis: Identification of the incorrect statement regarding Werner's Coordination Theory.
Step 1 (Governing Law & Definitions): [0.25 Mark]
According to Alfred Werner's Postulates for Coordination Compounds:
- Primary Valency: Corresponds to the oxidation state of the metal, is ionisable, and is satisfied by negative ions.
- Secondary Valency: Corresponds to the coordination number ($CN$), is non-ionisable, and is satisfied by neutral molecules or negative ions (ligands).
Step 2 (Step-by-Step Evaluation of Statements): [0.50 Mark]
- (A) are non-ionisable: Correct. Secondary valencies are directed towards fixed positions in space and do not dissociate in solution.
- (B) are ionisable: Incorrect. By definition, secondary valencies are non-ionisable. Ionisability is a characteristic of primary valencies.
- (C) are satisfied by neutral molecules or negative ions: Correct. These act as ligands donating electron pairs to the central metal.
- (D) is equal to the coordination number and is normally fixed for a metal: Correct. The number of ligands directly bonded to the metal is the $CN$, which remains constant for a specific complex.
Step 3 (Final Concluded Answer): [0.25 Mark]
The incorrect statement is (B).
💡 EL10 Concept Insight: Think of the primary valency like a loose handshake that can let go (ionisable), while the secondary valency is like a strong, permanent glue (non-ionisable) that holds the ligands tightly attached to the metal center in a specific shape.