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The increasing order of pKa of the following amino acids in aqueous solution is: Gly Asp Lys Arg

1. Asp < Gly < Arg < Lys
2. Gly < Asp < Arg < Lys
3. Asp < Gly < Lys < Arg
4. Arg < Lys < Gly < Asp

Correct answer: Asp < Gly < Arg < Lys

Solution

The pKa values of amino acids reflect their side chain acidity; as the order shows, aspartic acid has the lowest pKa due to its carboxyl group, followed by glycine, which has no charged side chain, then arginine, which has a basic side chain, and finally lysine, which has a higher pKa due to its more basic nature.

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