Among the following compounds most basic amino acid is:

Question

Canvas Classes · Accepted Answer

Basicity of amino acids depends on the number and pKa of basic groups:

| Amino acid | Basic groups | pKa of side chain |
|---|---|---|
| Lysine (Lys) | -NH₂ + -NH₂ | ~10.5 |
| Asparagine (Asn) | -NH₂ only (amide is non-basic) | — |
| Serine (Ser) | -NH₂ only (–OH is non-basic) | — |
| Histidine (His) | -NH₂ + imidazole | ~6.0 |

Reasoning:
- Lysine has two amino groups: the -amino group and the -amino group on the side chain (pKa ≈ 10.5)
- Histidine has an imidazole ring but its pKa (~6.0) is l

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