Which of the following is a natural dye?
(1) Crystal violet
(2) Aniline blue
(3) Alizarin
(4) Phenolphthalein
Answer: (3) Alizarin or 1,2-dihydroxyanthraquinone (also known as Mordant Red 11 and Turkey Red is an organic compound with formula C14 H8 O4 that has been used throughout history as a prominent red dye, principally for dyeing textile fabrics. Historically it was derived from the roots of plants of the madder genus. In 1869, it became the first natural pigment to be duplicated synthetically. Alizarin is the main ingredient for the manufacture of the madder lake pigments known to painters as Rose madder and Alizarin crimson. Alizarin is the most common usage of the term has a deep red color, but the term is also part of the name for several related non-red dyes, such as Alizarine Cyanine Green and Alizarine Brilliant Blue.
