When SO ₂ gas is bubbled through an acidified aqueous solution of K ₂ Cr ₂ O ₇ , the solution turns green due to the complete reduction of the chromium species. The spin-only magnetic moment (in Bohr Magnetons) of the transition metal ion present in the green product is:

Step-by-step solution

Sulfur dioxide ( SO ₂ ) reduces acidified potassium dichromate ( K ₂ Cr ₂ O ₇ ) to chromium(III) ions ( Cr ³⁺ ), which imparts the green colour to the solution. The oxidation state of chromium in the product is +3 . The atomic number of Cr is 24 , and its ground-state electronic configuration is [ Ar ] 3 d ^5 4 s ^1 . For the Cr ³⁺ ion, three electrons are removed (one from 4s and two from 3d), resulting in the configuration [ Ar ] 3 d ^3 . The number of unpaired electrons ( n ) in Cr ³⁺ is 3 . The spin-only magnet