Question

Acidic hydrogen is present in:
A. Ethyne
B. Ethene
C. Benzene
D. Ethane

Answer 1

Hint: For solving these types of questions we must know the definition of Acidic hydrogen. Also, we must know the molecular formula of given compounds.

Complete answer:
Acidic hydrogen is, it appears to be released as H+ ion. So if any H-atom is bound to another atom or group of atoms with higher electronegativity than that H-atom is a possible H-atom with acidity.
The acidity of the hydrogen atoms is directly proportional to the s-character.

Chemical compound	Formula	Hybridisation	% s- character
Ethane	$C{H_3} - C{H_3}$	$s{p^3}$	25%
Ethene	$C{H_2} = C{H_2}$	$s{p^2}$	33.33%
Ethyne	$CH$≡$CH$	$sp$	50%
Ethane	${C_6}{H_6}$	$s{p^2}$	33.33%

Ethyne has the highest percentage of s-character, and most acidic hydrogen atoms are found in ethyne.
We can observe that Ethyne is an alkyne with molecular formula ${C_2}{H_2}$which contains $sp$ hybridized carbon, Ethene is an alkene with molecular formula ${C_2}{H_4}$which contains $s{p^2}$ hybridized carbon, Benzene is a cyclic alkene with molecular formula ${C_6}{H_6}$ which contains $s{p^2}$hybridized carbon and Ethane is an alkane with molecular formula ${C_2}{H_6}$ which contains $s{p^3}$ hybridized carbon.
As s character is highest in $sp$ hybridized carbon, the electronegativity of carbon is highest because it lies close to the nucleus and removes electrons from hydrogen, releases ions easily and acts as acid.

Therefore, option A is correct and acidic hydrogen is present in ethyne.

Note: For solving these types of questions we must remember the property of $sp$, $s{p^2}$and $s{p^3}$ hybridized carbon atoms and the property of atoms. In this case we saw the ion releasing property of the hydrogen atom.