What is the hybridization of carbon atoms in ethyne?

Ethyne, also known as acetylene, has the chemical formula $\text{C}_2\text{H}_2$. Its structure is $\text{H}-\text{C}\equiv\text{C}-\text{H}$.

Each carbon atom in ethyne is involved in:

• One single bond (sigma bond) with a hydrogen atom.
• One triple bond with the other carbon atom. A triple bond consists of one sigma bond and two pi bonds.

For each carbon atom:

• Number of sigma bonds = 1 (to H) + 1 (to C) = 2
• Number of lone pairs = 0

The number of electron domains (sigma bonds + lone pairs) around each carbon atom is 2.

• 2 electron domains correspond to sp hybridization.
• 3 electron domains correspond to sp² hybridization.
• 4 electron domains correspond to sp³ hybridization.

Since each carbon atom in ethyne has 2 electron domains, its hybridization is sp.

The final answer is $\text{D}$.