Which valency is Ionisable?

Hint: In order to answer this question, first we will mention the name of valency which is ionisable, and then we will explain about the type of valency. And we will also give an example to make the term more understanding.

Complete answer:
Primary valency is known to be ionisable. The amount of negative ions necessary to fulfil the charge on a particular metal ion is known as primary valency. Outside of the coordination realm, it's usually written.
The oxidation state of the central metal atom in a coordination complex is known as primary valency. A coordination complex is a complex compound with a metal ion in the centre and several atoms or groups of atoms surrounding it. Ligands are the chemical species that surround the host.
Or in other words, the oxidation state of the central metal atom is primary valence, whereas the coordination number (number of ligands linked to the central metal atom) is secondary valence.
For eg.- \[{K_4}\left[ {Fe{{\left( {CN} \right)}_6}} \right]\]
where, the primary valency of \[Fe = + 2\]
The secondary valency or coordination number of \[Fe = 6\]
\[6C{N^ - }\] ions are attached directly to the $Fe$ metal ion.
Negative ions satisfy primary valencies, while neutral or -ve groups satisfy secondary valencies. The ligands in complexes are projected in space around the central metal atom to give the complex a characteristic form.

Note:
The number of negative ions connected to the core metal atom is known as primary valency. The number of ions or molecules that are coordinated to the central metal ion is known as secondary valency, or co-ordination number.