Question

Most acidic hydrogen is present in _________.

Answer 1

Ethyne

1. Hybridization is the intermixing of atomic orbitals of the same or different shapes and comparable energies to form new orbitals having the same energy and shape.
2. The carbon atom in ($\mathrm{H}-\mathrm{C}\equiv \mathrm{C}-\mathrm{H}$) Ethyne is $\mathrm{sp}$ hybridized.
3. And we know that the acidity of the hydrogen atoms is directly proportional to the percentage of s-character in that compound.
4. In other words we can say that the more the percentage of s-character is more will be the acidity of the hydrogen atom.
5. In Ethyne the percentage of s-character is $\frac{1}{2}\times 100=50\%$, thus it is the maximum and hence has the most acidic hydrogen atoms
6. Some other examples are:

Compound	Chemical formula	Hybridisation	% s-character
Ethane	${\mathrm{CH}}_3-{\mathrm{CH}}_3$	${\mathrm{sp}}^3$	$\frac{1}{4}\times 100=25\%$
Ethene	${\mathrm{CH}}_2={\mathrm{CH}}_2$	${\mathrm{sp}}^2$	$\frac{1}{3}\times 100=33.33\%$
Ethyne	$\mathrm{CH}\equiv \mathrm{CH}$	$\mathrm{sp}$	$\frac{1}{2}\times 100=50\%$

Therefore, most acidic hydrogen is present in Ethyne.