Which of the following postulates of Werner theory is incorrect?

The correct answer is Option (3) → The secondary valence is equal to the oxidation number of metal and is fixed for a metal.

Werner proposed that metals exhibit two types of valencies:

• Primary valency → Equal to oxidation state , Ionisable , Satisfied by negative ions

• Secondary valency → Equal to coordination number , Non-ionisable , Fixed spatial arrangement

Important:

Primary valency = Oxidation state

Secondary valency = Coordination number

They are NOT the same.

Option 1: In coordination compounds metals show two types of linkages (valences)-primary and secondary. This is a correct postulate of Werner theory.

Option 2: Primary valencies are ionisable and satisfied by negative ions. Correct according to Werner’s theory.

Option 3: States that secondary valency equals oxidation number. This is incorrect. Secondary valency = Coordination number Primary valency = Oxidation number Hence this statement is wrong

Option 4: The ions/groups bound by the secondary linkages to the metal have characteristic spatial arrangements corresponding to different coordination numbers. Correct postulate.