Which compound is classified as a hydrocarbon?
(1) butanal (3) 2-butanol
(2) butyne (4) 2-butanone

Answer: The correct answer is Option 2.Explanation:Hydrocarbons are defined as the compounds which have a covalent bond present between hydrogen and carbon atoms. For Example: [tex]CH_4[/tex] is a hydrocarbon. [tex]H_2O,CO_2[/tex] are not considered as hydrocarbons.For the given options:Option 1: butanalThe chemical formula for this compound is [tex]CH_3CH_2CH_2CHO[/tex]This is not considered as a hydrocarbon because a covalent bond is present between carbon and oxygen atom.Option 2: butyneThe chemical formula for this compound is [tex]CH\equiv CCH_2CH_3[/tex]This is considered as a hydrocarbon because covalent bonds are present between carbon and hydrogen atoms only. Option 3: 2-butanolThe chemical formula for this compound is [tex]CH_3CH(OH)-CH_2CH_3[/tex]This is not considered as a hydrocarbon because a covalent bond is present between carbon and oxygen atom. Option 4: 2-butanoneThe chemical formula for this compound is [tex]CH_3C(O)-CH_2CH_3[/tex]This is not considered as a hydrocarbon because a covalent bond is present between carbon and oxygen atom.From the above information, the correct answer is Option 2.

(2) butynu........................