Which of the following ions is colored due to d-d transitions?
Ni^{2+ (Z = 28): 3d⁸ . Partially filled d orbitals allow d-d transitions, causing a green color in aqueous solution. This follows from latest NCERT 2026-27 principle explaining the concept clearly for NEET students in simple steps as per rationalized syllabus.
Ref: NCERT Chemistry Textbook - Latest Edition for Academic Session 2026-27 (Rationalized Textbook for Class XI and XII), Chapter: Coordination Compounds and d Block Elements (Latest NCERT 2026-27), Topic: Colour of [Ti(H₂O)₆]³⁺, crystal field theory and d-d transition