Coal is formed by the decomposition of large land plants and trees that got buried under the earth millions of years ago. That is, it was believed that due to earthquakes and volcanoes, the forests were buried under the earth's surface and were covered with sand, clay and water. Due to high pressure and temperature inside the earth and in absence of air, the wood was converted into coal.

The crude oil is not a single chemical compound. It is a complex mixture of several solid, liquid and gaseous hydrocarbons mixed with salt, water and earth particles. Petroleum is the crude oil from which the fuels like LPG, diesel, kerosene and petrol are obtained.

What is denatured alcohol?

To prevent the misuse of industrial alcohol for drinking purpose, the ethanol meant for industrial purpose is denatured by adding small amounts of poisonous substance like copper sulphate or methanol or pyridine. This addition makes this ethanol unfit for drinking. This alcohol is called as denatured alcohol.

Isomers are the organic compounds having same molecular formula, but different arrangements of carbon atoms or simply different structures. For example, butane can exist in two isomeric forms such as n-butane and iso-butane.