When we switch on a torch, it gives light. The moment we switch off the torch, light goes off. What kind of change is it? Explain. 
 

Give reasons for the following:

Expansion and contraction are maximum in gases.

Give reasons for the following:

Silver pieces of jewellery tarnish when exposed to air.

Give reasons for the following:

Apples and some other fruits turn brown when cut surface is exposed to air.

Name the type of changes that occur in the burning of a candle. Explain with reason.

Name the type of change that occur during digestion of food. Explain with reason.