On what basis do curd formation from milk and ice formation from water differ? (Choose the correct basis.)

Correct answer: Curd forms by chemical change in which milk proteins coagulate due to acids; ice forms by physical change due to freezing when heat is removed

Curd formation from milk is due to bacterial activity that produces lactic acid. This acid causes milk proteins to coagulate, so curd formation is a chemical change. Ice formation from water happens when temperature is lowered enough that water freezes; this is a physical change because only the physical state (liquid to solid) changes. Hence the basis differs: \(\text{chemical change (acid + coagulation)}\) for curd and \(\text{physical change (freezing)}\) for ice.