Question

Formation of ethyne​

Answer 1

Ethyne is formed by the bonding of hydrogen and carbon atoms

Answer 2

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Ethyne is built from hydrogen atoms (1s1) and carbon atoms (1s22s22px12py1). The carbon atom doesn't have enough unpaired electrons to form four bonds (1 to the hydrogen and three to the other carbon), so it needs to promote one of the 2s2 pair into the empty 2pz orbital.