Which one of the following is an example of a chromoprotein?

Correct option is A

Haemoglobin is a classic example of a chromoprotein, which is a protein conjugated with a pigmented prosthetic group. In haemoglobin, the prosthetic group is heme, which contains iron and gives blood its red color. Chromoproteins play key roles in oxygen transport, light absorption, and electron transfer depending on the pigment involved.
Explanation of options: (a) Haemoglobin – This is the correct answer. It is a conjugated protein with an iron-containing heme pigment, classifying it as a chromoprotein essential for oxygen transport in blood. (b) Casein – This is a phosphoprotein found in milk. It helps in calcium and phosphate transport but is not pigmented and hence not a chromoprotein. (c) Mucin – Mucin is a glycoprotein that forms mucus, aiding in lubrication and protection of epithelial surfaces. It contains no pigment and is not a chromoprotein. (d) Glutenin – A storage protein found in wheat, contributing to dough elasticity. It is not associated with any pigment and does not qualify as a chromoprotein.