In aqueous solutions carboxyl group can lose protons and the amino group can accept a proton thus giving rise to a dipolar known as zwitter ion. Due to this dipolar behaviour they have strong electrostatic interactions within them. For this reason melting point of amino acids is high. It has more than one basic groups amine and guanidine, hence it has two pKa values. It is crystaline solid

Since arginine is polar, it is not soluble in benzene.