In combined state, carbon occurs as

1. coal
2. diamond
3. graphite
4. petroleum

Graphite is used to make crucibles because it is:

1. a good conductor of electricity
2. a good conductor of heat
3. soft and slippery
4. has high melting point

Diamond is used for

1. making the electrodes of electric furnaces.
2. making crucibles for melting metals.
3. cutting and drilling rocks and glass.
4. making carbon brushes for electric motors.

Carbon forms innumerable compounds because

1. it has four electrons in its outermost shell.
2. it behaves as a metal as well as a non-metal.
3. carbon atoms can form long chains.
4. it combines with other elements to form covalent compounds.