Lysine is a/an …………… amino acid and is ……… in nature.

The correct answer is Option (3) → essential, basic.

Amino acids are classified in two ways. By the number of amino and carboxyl groups in the molecule, they are neutral, acidic or basic. By nutrition, they are essential (the body cannot make them, so they must come from the diet) or non-essential (the body makes them).

Lysine, \( \ce{H2N-(CH2)4-CH(NH2)-COOH} \), has two amino groups and only one carboxyl group, so it is basic. The human body cannot make lysine, so it is an essential amino acid.

NCERT (2026-27 edition):
Classification of Amino Acids – “Amino acids are classified as acidic, basic or neutral depending upon the relative number of amino and carboxyl groups in their molecule. Equal number of amino and carboxyl groups makes it neutral; more number of amino than carboxyl groups makes it basic and more carboxyl groups as compared to amino groups makes it acidic. The amino acids, which can be synthesised in the body, are known as non-essential amino acids. On the other hand, those which cannot be synthesised in the body and must be obtained through diet, are known as essential amino acids (marked with asterisk in Table 10.2).”