The correct options are
A Catenation
B tetravalency
Catenation occurs when atoms of the same element covalently bond to one another. This self-linking property leads to the
formation of long chains and rings. Elements like carbon, sulphur, etc., show catenation.
Carbon has a valency of four because of which it can simultaneously bond with four other atoms. This property is shown by elements like carbon and silicon; and is called tetravalency.
However, allotropy and nuclear charge are not responsible for the formation of long chain carbon compounds.