Hello,
        In the case of [CrF₆]³⁻, Chromium has 3+ charge and total charge on 6 Fluorine atoms(1- for each Fluorine atom)is 6-. Anion shape is octahedral (or hexahedral?) due to 6 σ bonds formed between Fluorine and Chromium atoms. 

The type of hybridization is d²sp³.

I want to know which d, s and p orbitals are hybridized? and how many valence electrons of Cr takes part in hybridization? My guess for valence electrons of Cr is 15, but it has 12 electrons in the form of sigma bonds in its surrounding, so it get 3+ charge. What is the lewis dot structure of [CrF₆]³⁻?
If any member of this forum knows the answer, may answer these questions.

 Hello,
         I want to correct my guess about valence electrons of Chrmium. Valence electrons must be 9 electrons.

Hello,
Please read Chromium in reply#1. My 'O' letter key on my keyboard is not working properly.

 [CrF₆]³⁻
Name of the anion is Hexafluorochromate(III)
Chromium(+3) Electronic configuration is  [Ar] 3d³
It has only 3 valence electrons
Now fluoride is a weak field ligand and can not do strong splitting of t_2g and e_g orbitals
This results in filling of all three  t2g with one unpaired electron in each orbital and  eg orbitals are left vacant .Now two 3d orbitals (eg) and  4s and 4p (three ) hybridizes to accomodate 6 lone pairs from Fluoride ion 
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