Answer:
The end product of the Turnbull blue reaction is (b) potassium ferrous ferricyanide.
Step-by-step explanation:
The Turnbull blue reaction is a histological staining method used to demonstrate the presence of melanin in tissues. This staining technique involves treating tissue sections with a solution of potassium permanganate, which oxidizes melanin to form a brown pigment. The tissue sections are then treated with a reducing agent, such as oxalic acid or sodium bisulfite, which reduces the excess permanganate and produces a permanent blue-black color in the melanin. The blue-black pigment formed is called Turnbull blue.
Turnbull blue is then treated with potassium ferricyanide, which reduces it to potassium ferrous ferricyanide. The resulting compound is insoluble and produces a dark blue or black color.
Potassium ferric ferrocyanide and potassium ferricyanide are not end products of the Turnbull blue reaction. Potassium ferrocyanide is used to demonstrate the presence of ferric iron in tissues.