Which formula represents an alkyne? a) cnhn. b) c2nhn c) cnh2n + 2 d) cnh2n – 2

            Option-D is the correct answer.

Explanation:
                     Hydrocarbons are classified as;

a) Saturated Hydrocarbons:
                                           Those hydrocarbons in which all carbon atoms are bonded to each other through a single covalent bonds are known as Saturated Hydrocarbons.

                 Example:
                                Alkanes with a general formula CnH₂n+₂ belongs to saturated hydrocarbons. The Hydrogen Deficiency Index of Alkanes is zero, means it does not contain any double or triple bond.

                               i)  H₃C-CH₃    Ethane

                               ii)  H₃C-CH₂-CH₃    Propane

                               iii)  H₃C-CH₂-CH₂-CH₃    Butane

b) Unsaturated Hydrocarbons:
                                           Those hydrocarbons in which a double bond (Alkenes) or triple bond (Alkynes) is formed between two carbon atoms are called as unsaturated Hydrocarbons.

                 Example:
                                Alkene with a general formula CnH₂n belongs to unsaturated hydrocarbons. The minimum Hydrogen Deficiency Index of Alkenes is one, means it contain minimum one double bond.

                               i)  H₂C=CH₂    Ethene

                               ii)  H₂C=CH-CH₃    Propene

                               iii)  H₃C-CH=CH-CH₃    2-Butene

                                Alkyne with a general formula CnH₂n-₂ belongs to unsaturated hydrocarbons. The minimum Hydrogen Deficiency Index of Alkynes is two, means it contain minimum one triple bond.

                               i)  HC≡CH    Ethyne

                               ii)  HC≡C-CH₃    Propyne

                               iii)  H₃C-C≡C-CH₃    2-Butyne