Question

What is the type of hybridisation and the geometry respectively found in $\mathrm{[CoF_6]^{3-}$?}

• A. $d^3sp^3$ and pentagonal bipyramidal
• B. $sp^3d^2$ and octahedral
• C. $dsp^3$ and trigonal bipyramidal
• D. $dsp^2$ and pentagonal bipyramidal

Hint:

Weak field ligands generally form outer orbital complexes with $sp^3d^2$ hybridisation.

Answer 1

The Correct Option is B

Step 1: Oxidation state of cobalt.
In $\mathrm{[CoF_6]^{3-}}$, each fluoride ion has a charge of $-1$.
\[ x + 6(-1) = -3 \Rightarrow x = +3 \] So, cobalt is in +3 oxidation state.

Step 2: Nature of ligand.
Fluoride ($\mathrm{F^-}$) is a weak field ligand and does not cause pairing of electrons.

Step 3: Hybridisation and geometry.
Due to weak field ligands, outer orbital complex is formed using $sp^3d^2$ hybridisation, resulting in octahedral geometry.

Step 4: Conclusion.
Hence, the correct answer is (B) $sp^3d^2$ and octahedral.