JEE Main 2023 — Biomolecules Question with Solution

Arginine is an amino acid that has a basic side chain containing a guanidino group. The other three options are true for arginine:

(A) It has a fairly high melting point due to the presence of strong ionic interactions between the positively charged guanidino group and the negatively charged carboxylate group in the solid state.

(B) It is associated with more than one pKa values because it contains multiple ionizable groups, including the amino group, the carboxylate group, and the guanidino group. These groups can dissociate in a stepwise manner, leading to multiple pKa values.

(D) It is a crystalline solid due to the presence of strong ionic interactions between the positively charged guanidino group and the negatively charged carboxylate group, which leads to the formation of a well-ordered crystal lattice.

However, option (C) is not true because arginine is not soluble in benzene. This is because benzene is a nonpolar solvent, and arginine is a polar and charged molecule. Therefore, arginine is more soluble in polar solvents such as water and less soluble in nonpolar solvents such as benzene.