The correct option is A Formation of curd from milk
Chemical changes involve change in the chemical composition of the original substance resulting into the formation of a new substance.
Among the given options formation of curd from milk is a chemical change, as the enzymes secreted by the bacteria converts milk into a new substance called curd.
The dissolution of sugar in water, cutting of paper and melting of ice are examples of a physical change as there is no change in the chemical composition of these substances.