Question

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

Hint:

Primary valency = the metal's charge, balanced by anions; secondary valency = coordination number.

Answer 1

The Correct Option is C

Concept: Werner studied metal complexes and said a metal uses two kinds of valency at once. The primary valency is just the charge on the metal ion, and the secondary valency is the number of groups sitting directly on the metal. To answer this we only need to remember what the primary valency really is.

Step 1: What is the primary valency
Think of the metal ion as a positive charge. That positive charge is the primary valency. Now any positive charge cannot stay alone, it needs negative charge to balance it. So the primary valency is always balanced by negative ions.

Step 2: Why those negative ions are special
These negative ions sit a bit away from the metal and can leave the metal when the complex is put in water. Because they can move away as free ions, we say the primary valency is ionisable.

Step 3: Why the other options describe the secondary valency
The choices that say 'equal to the coordination number' or 'satisfied by neutral molecules' are talking about the secondary valency, not the primary one. The secondary valency is the number of ligands joined to the metal, and those ligands stay fixed, so do not get confused between the two.

Step 4: Pick the right option
Since the primary valency is the metal's charge and is balanced by negative ions, the matching choice is the one that says it is satisfied by negative ions.

Answer: Option (C), the primary valency is the metal's charge and is satisfied by negative ions.