An orange solution of acidified potassium dichromate is treated with SO ₂ gas, resulting in the formation of a green-coloured transition metal species. The spin-only magnetic moment (in BM) of the transition metal ion present in the green-coloured product is closest to:

Step-by-step solution

When acidified potassium dichromate ( K ₂ Cr ₂ O ₇ ) is treated with SO ₂ gas, the dichromate ion ( Cr ⁶⁺ ) is reduced to the chromium(III) ion ( Cr ³⁺ ), which imparts a green colour to the solution. The electronic configuration of a neutral Cr atom is [ Ar ] 3d^5 4s^1 . For the Cr ³⁺ ion, three electrons are removed (one from 4s and two from 3d ), resulting in the configuration [ Ar ] 3d^3 . The number of unpaired electrons ( n ) in Cr ³⁺ is 3 . The spin-only magnetic moment ( ) is calculated using the formula: =