Identify A and B in the given sequence of reaction. Also, write their IUPAC names and calculate spin only magnetic moment of B.
`Fe^(3+)("aq")overset("Excess of"SCN^(theta))rarr"Blood red colour (A)"`
`overset("Excess of"F^(-))rarr"Colourless (B)"`

Explanation

The given reaction sequence is
`Fe^(3+)("aq")+underset("Excess")(SCN^(-))rarrunderset("Colour (A)")underset("Blood red")(Fe(SCN)_(3))`
`Fe^(3+)("aq")overset("Excess of"F^(-))rarrunderset("Colourless (B)")([FeF_(6)]^(3-))`
A-trithiocyanoferrum (III)
B-hexaflouroferrate (III) ion
IN `[FeF_(6)]^(3-),Fe^(3+)` has configuration `3d^(5),F^(-)` being weak field ligand and thus it cannot pair up the electrons and `[FeF_(6)]^(3-)` show `sp^(3)d^(2)` -hybridisation to possess octahedral shape with five unpaired eelctrons.
Thus, spin magnetic moment `=sqrt(n(n+2))` BM
`"BM"=sqrt(5xx(5+2))" BM"rArrsqrt(35)=5.92` BM