In the sequence of reactions
`Fe^(3+) (aq) underset(SCN^(-))overset("Excess of")rarr underset(("A"))("Blood red colour")underset(F^(-))overset("Excess of")rarr underset(("B"))("Colourless")`
Identify A and B. Write their IUPAC names. Explain the hybridisation involved in B and calculate spin only magnetic moment of B.

Explanation

`Fe^(3+)(aq)+3SCN^(-)rarr underset("Trithiocyanato iron (III)")underset(("A"))underset("Blood red colour")([Fe(SCN)_(3)])underset(F^(-))overset("Excess of")rarr underset("Hexafluoridoferrate (III)")underset(("B"))underset("Colourless")([FeF_(6)]^(3-))`
Hybridisation in `[FeF_(6)]^(3-)=sp^(3)d^(2) " " (because F^(-) " is a weak ligand")`
In `[FeF_(6)]^(3-), Fe^(3+)` has the configuration `3d^(5)`, i.e., it has 5 unpaired electrons.
`therefore` Magnetic moment `= sqrt(n(n+2))=sqrt(5(5+2))=sqrt(35)=5.92` BM.