Here's a detailed explanation:

In a carbon-carbon triple bond, the two carbon atoms share three pairs of electrons, forming a very strong and rigid bond. This bond can be represented as C≡C.

The sigma bond is formed by the head-on overlap of the two sp hybridized orbitals, one from each carbon atom. This results in a strong covalent bond that holds the two carbon atoms together along the internuclear axis.

In addition to the sigma bond, there are two pi bonds in a carbon-carbon triple bond. Pi bonds are formed by the sideways overlap of two p orbitals, one from each carbon atom. These p orbitals are perpendicular to the internuclear axis and to each other.

The pi bonds in ethyne are formed by the overlap of the two remaining p orbitals on each carbon atom. These p orbitals are oriented perpendicular to the sigma bond and to each other, creating two regions of electron density above and below the plane of the sigma bond.

The combination of the sigma bond and the two pi bonds in ethyne results in a very strong and rigid carbon-carbon triple bond. This bond is shorter and stronger than a carbon-carbon double bond or a carbon-carbon single bond. It also restricts the rotation of the two carbon atoms around the bond axis, making the molecule more rigid.

The presence of the triple bond in ethyne gives the molecule its unique chemical properties and reactivity. It is highly unsaturated and can undergo various addition reactions, where other atoms or groups of atoms can add to the carbon-carbon triple bond, breaking the pi bonds and forming new sigma bonds.