For a neutral amino acid $\left(X\right)$, the isoelectric point is 5.8. Now its solubility at this point in water is

The intermediate $\mathrm{pH}$ at which a protein molecule has a net charge of zero that point is called the isoelectric point of that protein.

It is also a fact that when protein or nucleic acid has a charge either positive or negative its interaction increases and thus the solubility.

Since the amino acid is at its isoelectronic point i.e neutral hence no charge on it. The solubility is minimum.

Hence option B is the correct answer.