A change which is useful to us is a _________ change.

The change which take longer time to occur are called ___________ change.

The changes which repeat themselves at regular intervals of time are called __________ changes.

Curdling of milk is an __________ reaction.

___________ is the process where a solid turns directly into gas without entering to the liquid liquid slate.

The formation of brown powdery material on the surface of iron in the presence of moisture is called 

The formation of frost is 

________ was developed by French Scientist Louis Pasteur.

Tooth decay is an example of _________ change.

Ripening of fruits is a __________ change.