Sonu' s mother served a glass of hot milk before his going to school.As sonu was in a hurry he forgot to drink the milk. Unfortunately his mother has also gone out. When they came back home, sonu noticed the changes in the milk,which was no more a milk,but set into a thick substance called curd.

Based on this situation answer the following questions:

a. What is this process of setting milk into curd known as?Is this a physical/chemical change?

b. Is this change harmful ?

c. How does it happen?

Its your choice that whether you want to answer all the 3 questions or just 2 of them.