<u>Answer:</u> The correct answer is Option 2.
<u>Explanation:</u>
Hydrocarbons are defined as the compounds which have a covalent bond present between hydrogen and carbon atoms. For Example:
is a hydrocarbon.
are not considered as hydrocarbons.
For the given options:
<u>Option 1:</u> butanal
The chemical formula for this compound is 
This is not considered as a hydrocarbon because a covalent bond is present between carbon and oxygen atom.
<u>Option 2:</u> butyne
The chemical formula for this compound is 
This is considered as a hydrocarbon because covalent bonds are present between carbon and hydrogen atoms only.
<u>Option 3:</u> 2-butanol
The chemical formula for this compound is 
This is not considered as a hydrocarbon because a covalent bond is present between carbon and oxygen atom.
<u>Option 4:</u> 2-butanone
The chemical formula for this compound is 
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.