Allotropy is the property of the element, when the element occurs in nature in more than one form with same chemical properties but different physical properties. Diamond, graphite and fullerenes are the three crystalline allotropes of carbon. All three allotropes have a definite geometrical shape with sharp edges and plane surfaces.

Limewater turns milky when CO2 is passed through it, due to the formation of calcium carbonate.

 Inside each layer of graphite, free electrons move continuously within the entire layer. This is the reason why graphite is a good conductor of electricity.

In the crystalline form of carbon, the atoms are arranged in a regular and definite manner. The melting and boiling points are pretty high for these. These also have definite geometrical shapes and have sharp edges and plane surfaces. There are three crystalline allotropes for carbon-Diamond, Graphite and Fullerene. Meanwhile, the arrangement of carbon atoms in non-crystalline forms of carbon is not regular. The non-crystalline forms of carbon include coal, charcoal, coke and so on.

Every carbon atom in diamond forms covalent bonds with four of its neighbouring atoms. So, diamond has a tetragonal three dimensional structure that makes it very hard. Meanwhile, every carbon atom in graphite bonds to three other carbon atoms to form a hexagonal layered structure. Graphite crystal is made of several sheets or layers of carbon atoms, which slip over others if pressure is applied. One layer of graphite is known as graphene.

Given below are certain uses for diamond:

• Cut glass and used in rock drilling machines.
• Used as ornaments.
• Used in the eye surgery.
• For Polishing other diamonds.
• Used to make windows to protect from radiation in space and in artificial satellites

 Carbon in free state is found as Diamond and Graphite. Meanwhile, Carbon is found in the combined state in the following compounds:

1. As carbon dioxide (CO2) and in the form of carbonates such as calcium carbonate, marble, calamine (ZnCO3)

2. Coal, Petroleum and Natural gas used as fossil fuels

3. Carbohydrates, Proteins and Fats used as Carbonaceous nutrients

4. Cotton, Wool and Silk as Natural fibres

The reasons why carbon and its compounds are used as fuels are given below:

1) Carbon and its compounds produces a lot of heat and light when burnt in air, as it contains large amounts of carbon and hydrogen

2) Saturated hydrocarbons do not produce any smoke and burns with a clean flame

3) Carbons that are used as fuels has the optimum ignition temperature

4) Carbon used as fuel have high calorific value

5) Combustion can be easily controlled

There are some microorganisms that cause disease in plants like wheat, sugarcane, rice, potato, orange, and apple. Like citrus canker disease caused by bacteria in plant, rust of wheat disease in wheat plant caused by fungi. These diseases reduce the yield of crops and can be controlled by using certain chemicals that kill microbes.