The most abundant protein in the animal world is

The correct option is Collagen.

To understand why this is the correct answer, let's break down the details of collagen and the other proteins listed in the options:
1. Collagen: This is a structural protein found abundantly in the extracellular matrix and connective tissues of animals (such as skin, bones, tendons, ligaments, and cartilage). It makes up about 25% to 35% of the whole-body protein content in mammals, making it the most abundant protein in the animal kingdom.
2. Trypsin: This is a digestive enzyme (protease) produced in the pancreas of animals. While essential for digestion, it is not present in structural quantities.
3. Haemoglobin: This is an iron-containing oxygen-transport metalloprotein found in the red blood cells of almost all vertebrates. Though abundant in blood, its overall quantity in the animal body is much less compared to structural proteins like collagen.
4. Insulin: This is a peptide hormone produced by beta cells of the pancreatic islets. It is a signaling molecule and is present in extremely minute (regulatory) quantities in the body.

Therefore, because of its widespread structural role across various connective tissues in all animals, Collagen is the most abundant protein in the animal world.