Answer:
According to the valence bond theory the triple bond in ethyne consists of one sigma bond and two pi bonds.
Explanation:
Atomic number of carbon is 6. The ground state electronic configuration of carbon is as follow,
1s², 2s², 2p²
And the excited state electronic configuration of carbon is as follow,
1s², 2s¹, 2px¹, 2py¹, 2pz¹
In ethyne the 2s¹ orbital and 2px¹ orbitals having unpaired electrons form sigma bonds by head to head overlapping with orbitals of hydrogen atom and carbon atom. The remaining 2py¹ and 2pz¹ orbitals of both carbons overlap perpendicular to the existing sigma bond resulting in the formation of two pi bonds.
