See image — AITS & Test Series Chemistry Question

💡 Solution & Explanation

At pH < isoelectric pH, –NH2 group is protonated to 3 NH   and the sol is positively charged. At pH > isoelectric pH, –COOH is deprotonated to –COO– and the sol is negatively charged. At isoelectric pH both groups are equally ionised, the sol particles carry no net charge.