Question

how many bond have to be there in between the two carbon atom in ethyne so as to satisfy their tetravalency

Answer 1

Ethyne is C2H2. The "yne" ending tells you that there is a triple bond between the two carbon atoms. (A double bond would be ethene; a single bond = ethane). Each covalent bond contains 2 electrons - one from each of the atoms that are involved

Answer 2

Answer:

Carbon is tetravalent in stable compounds. The chemistry can involve both bond breaking and making simultaneously. It can depend on the solvent.

Here is an example of alkene addition.