It is an organic compound containing two keto groups. It is used in the formation of many dyes and is used in bleaching the pulp used in paper making.Complete step by step solution:
> Alizarin is a red coloured crystalline compound. Earlier it was prepared from madder but nowadays it can be synthesized artificially. It is used to dye turkey red and is used in making red coloured pigments.
> Alizarin is an example of anthraquinone dye. It gives red colour with aluminium and blue colour with barium. Anthraquinone is a yellow coloured crystalline solid. It is poorly soluble in water but becomes soluble in hot organic solvents. Its IUPAC name is 9,10-diphenylanthracene. It is aromatic in nature.
> Azo dyes contain two N atoms in them. They contain C-N=N-C linkage. They are widely used in the textile industry, leather industry, etc.
> Trials are a group of synthetically prepared dyes. They contain the triphenylmethane backbone. Because of their reversible reaction with acid-base, they are used as pH indicators also.
- The structure of Alizarin is given below-
So, now we know about all the types of dyes given in the question.
Now, we conclude that Alizarin is an example of anthraquinone dye.
Hence, the answer to the given question is option (D)
Note: Alizarin is used for the detection of calcium in tissue sections. It is also used to identify cultured cells. It was the first naturally occurring dye which was later produced synthetically.