Question

What is secondary valence and how to determine the secondary valence of coordinate compounds?

Answer 1

Secondary valency = It is  the number ions or molecules directly attached or coordinated to the central metal atom.

The secondary valency of coordinate compounds can be calculated by counting number of molecules attached to central metal atom of coordination compound.
Example - [Cr$(H_2 O)_{6}$ ]$Cl_{3}$ 
                                                               has secoundary valancy = 6

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