1)Substances that burn easily or catch fire easily is called a combustible substance.
Examples are LPG ,wood,paper etc.....
4)Usually fuels are classified into three categories
Examples of solid fuels are wood,paper,clothes etc..
Examples of liquid fuels are kerosene,oil etc...
Examples of gaseous fuels are Biogas,hydrogen etc...
5)The various pollutants emitted when fossil fuels are burnt are carbon monoxide,carbon dioxide,sulphur dioxide,nitrogen oxides etc.......
The burning of fossil fuels lead to air pollution.The high concentration of CO2 leads to global warming which will cause many harmful effects.
Carbon monoxide combines with haemoglobin in the blood to form carboxy-haemoglobin which will block the blood from transporting oxygen.
Burning of fossil fuels emit sulphur dioxide and nitrogen oxides which will cause acid rains.
They also cause many respiratory problems.