Question

Which of the following compounds is most acidic?
(A) \[C{H_4}\]
(B) \[{C_2}{H_6}\]
(C) \[CH \equiv CH\]
(D) \[{C_2}{H_5}OH\]

Answer 1

Hint: Acidic strength in organic acids can be compared on the basis of their ability to donate protons and form stable anions after proton removal. The conjugate base that is formed as a result of proton removal contains negative charge that needs to be stabilized in order to make an organic compound acidic.

Complete Step By Step Answer:
Organic compounds can show acidic properties due to their ability to lose protons and form corresponding anions that are stable. The acidity is influenced by a variety of factors like the hybridization of the carbon atoms involved, the electronegativity of the atom to which the proton is attached and the presence of any acidic functional group.
Methane and ethane are alkanes in which the carbon atoms are saturated and have \[s{p^3}\] hybridization. With the least s-character in their orbitals, methane and ethane are poor acids in which the carbon atoms are not electronegative enough to stabilize the conjugate base anions.
Ethyne is an unsaturated compound consisting of triple bonds due to which both carbon atoms are in \[sp\] hybridization which has the highest s-character and sufficient electronegativity to stabilize the conjugate base formed after proton removal. But ethanol contains the alcohol functional group which is known for its acidic character. The proton in alcohols is attached to an oxygen atom which is highly electronegative and therefore provides maximum stability to the anion formed after proton removal,
\[ \Rightarrow \] Hence, out of all the given options ethanol \[{C_2}{H_5}OH\] is the most acidic compound.
Option (D) is correct.

Note:
The hybridization is an important factor in comparing acidic strength when we are dealing with the same element. Carbon atoms can never have more electronegativity than oxygen atoms irrespective of its hybridization.