The water soluble protein is:

Proteins may be broadly classified on the basis of their solubility. We have globular proteins that readily dissolve in water and fibrous proteins that are either sparingly soluble or completely insoluble. Albumins fall in the first category, while fibrin, myosin and collagen belong to the second.

Now, albumin is a globular protein. Being globular, its peptide chains fold in such a manner that the hydrophilic (water-loving) side chains remain on the outside of the molecule, whereas the hydrophobic (water-repelling) residues are tucked inside. So the overall interaction with water is favorable, and the protein dissolves.

In contrast, fibrin, myosin and collagen are fibrous proteins. Their long, extended chains align alongside one another, forming fibers or sheets. The exposed side chains are largely non-polar, offering very little scope for hydrogen bonding with water molecules. Hence they either do not dissolve or swell only slightly in water.

Comparing the four options, only albumin satisfies the condition of being water soluble.

Hence, the correct answer is Option B.