The valency of carbon is four.

Carbon is commonly present in petroleum, fabrics and proteins.

Due to the slippery nature of any two layers of graphite, it is used as a lubricant.

5 and 6 membered carbon rings are present in a molecule of C₆₀.

In the structure of diamond, each carbon atom is bonded to four other carbon atoms by covalent bonds.

The correct option is (3).

Alkenes are the carbon compounds with at least one double covalent bond between their carbon atoms. Double covalent bonds are formed when each atom contributes two electrons. Carbon cannot form a double covalent bond with hydrogen as hydrogen has only one valence electron. Therefore, alkene containing one carbon (i.e. methane) does not exist. The minimum number of carbon atoms that must be present in an alkene is two. Ethene (C₂H₄) is the simplest alkene containing two carbon atoms. 

The correct option is (1).

The correct option is (2).

Carbon black is used as a pigment in inks, paints and plastics.