In aqueous solution near neutral pH, an amino acid such as glycine exists mainly as ____.
Correct answer B. A zwitterion, ⁺H₃N–CH₂–COO⁻
Explanation
The acidic –COOH group donates a proton to the basic –NH₂ group within the same molecule, forming a dipolar ion with both positive and negative charges but no net charge. This explains the high melting points of amino acids.
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