Answer
When a substance appears to be yellow, it is absorbing light from the blue-violet, high energy end of the visible spectrum. Often this absorption is just the tail of a strong absorption in the ultraviolet. Substances that appear green or blue to the eye are absorbing light from the lower energy red or orange part of the spectrum.
Cyanide ion is a very strong field ligand. It causes a higher crystal field splitting than water, resulting in the absorption of higher energy (shorter wavelength) radiation when a d-electron is excited to a higher energy d-orbital.
Work Step by Step
When a substance appears to be yellow, it is absorbing light from the blue-violet, high energy end of the visible spectrum. Often this absorption is just the tail of a strong absorption in the ultraviolet. Substances that appear green or blue to the eye are absorbing light from the lower energy red or orange part of the spectrum.
Cyanide ion is a very strong field ligand. It causes a higher crystal field splitting than water, resulting in the absorption of higher energy (shorter wavelength) radiation when a d-electron is excited to a higher energy d-orbital.
