UPSC Combined Geo-Scientist, Mains · 2026 · Mains Paper I
Q2(b). Assignment of the spectrum of [Cr(NCS)₆]³⁻
Question
The spectrum of [Cr(NCS)₆]³⁻ has a very weak band near 16000 cm⁻¹, a band at 17700 cm⁻¹ with ε_(max)=160 dm³ mol⁻¹ cm⁻¹, a band at 23800 cm⁻¹ with ε_(max)=130 dm³ mol⁻¹ cm⁻¹, a very strong band at 32400 cm⁻¹. Assign these transitions, using selection rule considerations.
Model answer
The free solution for 2026 answers the questions picked in its time plan. Question 2 is answered in full in the Book Edition of the 2026 solutions of Geo-Scientist Chemistry Paper I.
Coversd³ spectraAssignment of the spectrum of [Cr(NCS)₆]³⁻
All parts of Question 2
- 2(a) SrCl₂ or CdCl₂: fluorite structure10 marks
- 2(b) Assignment of the spectrum of [Cr(NCS)₆]³⁻10 marks
- 2(c) Magnetism and isomers of M(PR₃)₂Cl₂ (M = Ni, Pd)10 marks