Which process is a chemical change?
(1) melting of ice
(2) boiling of water
(3) subliming of ice
(4) decomposing of water

Option 4 = decomposing of water

Explanation:

Chemical change:

The changes, that occur due to change in the composition of a substance and result in a different compound is known as chemical change.

These changes are irreversible .

These changes occur due to chemical reactions .

These may not be observed with naked eye .

Example:

Combustion of fuel or wood: that oil or wood convert into energy, CO2 and ash in case of wood

Boiling of egg: that change the chemical composition of protein in the egg

The reaction of Hydrogen and oxygen:

H 2 (g)  + O 2  (g) > 2H 2O  (l)

Physical Change                                                                                              

The changes that occur only due to change in shape or form but their chemical or internal composition remain unchanged.

These changes were reversible.

They have same chemical property.

These changes can be observed with naked eye.

Example

Water converting to Ice .

Water converting to gas .

In this water molecule remain the same only they rearrange themselves that change its state of mater not composition .

1 = Melting of ice

The melting of ice is physical change because water molecules are just change the state from solid to liquid and composition remain same.

2 = Boiling of water

It is also a physical change because water molecules are just change the state from liquid to gas and the molecular structure of water molecules remain same.

3 = Subliming of ice

It is physical change because ice is converted into water vapors without going through liquid phase.

4 = Decomposing of water

It is a chemical change because water molecules are split into the hydrogen and oxygen. The molecular structure is changed. New product is formed which is different from the reactant.