Setting Curd from Milk: A Physical Change
Setting curd from milk is an example of a physical change. Let's understand this process in detail.

Physical Change:
- A physical change is a change in which the substance undergoes a change in its physical state without altering its chemical composition.
- When curd is set from milk, the milk changes from a liquid state to a semi-solid state without any change in its chemical composition.

Process of Setting Curd:
- The process of setting curd involves adding a small amount of curd (which contains live bacteria) to warm milk.
- The live bacteria present in the curd convert lactose (a sugar present in milk) into lactic acid through the process of fermentation.
- This lactic acid then coagulates the milk proteins, causing it to thicken and form curd.

Physical Changes in Setting Curd:
- The physical changes that occur during the setting of curd include the thickening of milk, formation of curd, and separation of whey (liquid portion).
- The chemical composition of the milk remains the same, but its physical state changes from liquid to semi-solid.

Conclusion:
Setting curd from milk is a physical change as it involves a change in the physical state of the substance without altering its chemical composition. This process is widely used in households and industries to produce curd, which is a nutritious dairy product.

Chemical change