Products formed when methane burns in air:

When methane (CH4) burns in air, it undergoes a combustion reaction and reacts with oxygen (O2) to form new substances. The products formed are carbon dioxide (CO2) and water (H2O). Additionally, heat is released during this exothermic reaction.

The balanced chemical equation for the combustion of methane:
CH4 + 2O2 → CO2 + 2H2O

Now let's break down the process and understand it in detail:

1. Combustion reaction:
Combustion is a chemical reaction that occurs when a substance reacts with oxygen, typically producing heat and light. When methane burns in air, it combines with oxygen to produce new compounds.

2. Reactants:
- Methane (CH4): Methane is a hydrocarbon, which means it consists of carbon and hydrogen atoms. It is a flammable gas commonly found in natural gas and is widely used as a fuel.
- Oxygen (O2): Oxygen is a gas that is essential for combustion to occur. It supports the burning process by providing the necessary reactant.

3. Products:
- Carbon dioxide (CO2): When methane reacts with oxygen, one carbon atom from methane combines with two oxygen atoms from oxygen gas to form carbon dioxide. Carbon dioxide is a greenhouse gas and a byproduct of many combustion processes.
- Water (H2O): The four hydrogen atoms from methane combine with two oxygen atoms from oxygen gas to form two molecules of water. Water is a stable compound and exists as a liquid under standard conditions.

4. Heat release:
The combustion of methane is an exothermic reaction, which means it releases heat. This heat is a result of the breaking of chemical bonds in methane and the formation of new bonds in carbon dioxide and water.

Therefore, the correct answer is option 'A': CO2 + 2H2O + heat.