Step 1: Understanding the Concept:
Proteins are divided by shape into fibrous proteins (long thread-like chains, insoluble in water) and globular proteins (coiled into a ball shape, soluble in water).
Step 2: Key Formula or Approach:
Fibrous examples: keratin (hair, nails, wool), myosin, collagen, fibroin. Globular examples: insulin, albumins, haemoglobin, enzymes.
Step 3: Detailed Explanation:
Serum albumin, insulin and egg albumin are all water soluble globular proteins.
Keratin has chains lying side by side, held by hydrogen bonds and disulphide bridges. It is insoluble in water, and it is a fibrous protein.
Final Answer:
Keratin is not a globular protein, option (D).
\[ \boxed{\text{Keratin}} \]