Most abundant in bone -: (A) Arginine, (B) Hydroxyproline, (C) Proline, (D) Alanine
Answer is B. Most abundant protein in bones is collagen. Collagen is formed from glycine proline lysine Proline and lysine are hydroxylated to make OH-proline and OH-lysine. Now, you have to choose between option 2 and 3. As most of the proline in collagen is hydroxyated so best out of these two options is hydroxyproline. Extra information: OH-proline cause extensive hydrogen bonding and hence collagen provide strength to the bones.