Hint: Amino acids are organic compounds containing amine and carboxyl functional groups along with a side chain specific to each amino acid. So amino acid is made up of Carbon, hydrogen, oxygen, nitrogen and other elements are found in side chains of some amino acids. Side chain of amino acid resembles ammonia which is a base.Complete step by step solution:
> There are three amino acids that have basic side chains at neutral \[pH\] . These are arginine, histidine, lysine. Their side chains contain nitrogen. Lysine is used in the biosynthesis of proteins, It contains an $\alpha - $ amino group , $\alpha - $ carboxylic acid group, and a side chain lysyl. Lysyl is a basic charged aliphatic amino acid. It has two amine groups.
> Asparagine is an $\alpha $- amino acid that is also used in biosynthesis of proteins. A side chain of carboxamide distributes it as a polar aliphatic amino acid. Serine contains an alcohol and is functionally important in many proteins. It is useful for metabolism of fat, fatty acid and cell membranes and a healthy immune system. Histidine is an alpha-amino acid with an imidazole functional group. So as it contains the most basic nitrogen atom, it is the most basic amino acid. Hence option D is correct.
Note: We know that amino acids are known as ‘building blocks’ of proteins. It assists in the growth of muscles, connective tissues, tissue strength and maintains healthy skin. It has healing and repair capabilities in our body. Here histidine is most basic among all the given options because it contains imidazole.