Changing of water vapour into water is called condensation.

Periodic change - A change that occurs during a definite time interval is known as periodic change, e.g. phases of moon.

Heating of milk for boiling to kill microbes is known as pasteurization. Milk is prevented from spoilage for several days by pasteurization.

Yes, it is a fast change. The changes which take less  time are called fast changes.

Changes in which physical properties like shape, size and state change without formation of new substance are called physical changes.

Petrol can catch fire very easily with a single spark or flame because its ignation temperature is low. Hence, it is an  inflammable substance.

The melting of an ice candy is a reversible change because ice candy melts due to increased temperature (room temp).

When a state change occurs from solid to liquid, particles gain energy.

A reversible change is a change that can be undone or reversed, so a piece of iron is heated to red hot and tis softens it. It is then beaten into the desired shape. It is a reversible change.

In which the molecule present in the food undergoes change to form molecule.

Changes that cannot be reversed are called irreversible changes.

because plaster of Paris has a property of setting into a hard mass on getting mixed with water due to the formation of a new compound. The hard mass cannot be converted back into the previous plaster of Paris.

Changes that can be reversed is called reversible changes.

Changes that cannot be reversed are called irreversible changes. Milk changes into curd

To prevent them from spoilage, they are stored at low temperature in a refrigerator where microbes are unable to survive. Lowest level of the refrigerator will prevent them from contaminating other foods.