Question

Can you explain (every small detail) about the hybridisation of Cr in K2Cr2O7 being d3s? Why d3s and not d5?

Answer 1

The Cr(2)O(7)2−is a special coumpound.

The Oxidation state of Cr is +6.

Also no electrons are available in valence shell of Cr+6 ie it has empty 4s and 3d subshell. Three 3d orbitals ie. 3dxy, 3dyz and 3dzx and One 4s orbital is used.

If you wonder why other orbitals of the d doesn’t come into picture is because they are at high energy level (CFT theory) and it’s easier to form bond with it.

So this makes the hybridisation as d3s.

since you asked small details i have given answer in a short way