Is it true that the formation of curd from milk is a reversible change? 

A reversible change is one that can be reversed or undone. These changes are visible in the substance's physical state, size, and shape. A reversible change does not result in the formation of a new material. An irreversible change, on the other hand, is one that cannot be reversed or returned to its original state. Because we can't reverse the formation of curd from milk, it's an irreversible change, which means we can't make milk from curd.