Answer: Option (a) is the correct answer.
Explanation:
The isoelectric point (pI) is actually the pH where a particular amino acid exists as a neutral molecule. This means that if pH equals pI then there will be no electric charge on the molecule.
Therefore, the statement at pH near the pI, nearly all the molecules carry no net charge, is true.
A buffer is composed of a solution of weak acid or base and salt of weak acid/base.So, when pH equals pI then there occurs no net charge. Hence, there will be no existence of conjugate acid-base pair.
Therefore, the statement when the pH is near the pI, the solution is near its maximum buffering ability, is false.
It is known that when pH is less than pI then there will be a net positive charge on the amino acid.
Hence, the statement at a pH near the pI, nearly all the molecules carry a net positive charge, is false.
When pH is greater than pI then amino acid will have a net negative charge. Hence, the statement at a pH near the pI, nearly all the molecules carry a net negative charge, is false.
Thus, we can conclude that out of the given options the statement at pH near the pI, nearly all the molecules carry no net charge, is true.
