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JEE Main levelSingle correct optionDifficulty 2 of 3bm189

For glycine, $p K_{a 1}$ ( $- COOH$ ) $= 2.34$ and $p K_{a 2}$ ( $- NH X_{3} X^{+}$ ) $= 9.60$ . Taking the isoelectric point as the mean of the two pKa values flanking the neutral species, pI is

A2.34
B9.60
C5.97
D11.94

Answer: C

The neutral zwitterion lies between the two ionisations, so pI = (2.34 + 9.60)/2 = 5.97.

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