Question

differentiate between chemical combination and decomposition. give examples.

[in a tabular form}

Answer 1

Combination reaction are those in which two reactants combine together to form a single product.
Example hydrogen+oxygen=water
Decomposition reaction are those in which a single material decomposes to form one or more product. It can take place when energy is provided in the form of heat, light or electricity. It's the opposite of combination reaction.
Example, water decomposes in presence of electricity to form hydrogen and oxygen.

Answer 2

When two or more substances combine together to form a new single substance is called combination reaction. For e.g.,
N2 + O2 gives out 2NO

When a single substance decomposes to form two or more substances is called decomposition reaction. For e.g.,
CaCO3 gives out CaO + CO2

These two reactions are just opposite to each other.