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Q.
According to molecular orbital theory, there are_____ $\pi$ bonds in $C_{2}$ molecule.
Chemical Bonding and Molecular Structure
Solution:
$C _{2}: \sigma 1 s ^{2}\, \sigma^{*} 1 s ^{2}\, \sigma 2 s ^{2}\, \sigma^{*} 2 s ^{2} \,\pi 2 p _{ x }^{2}=\pi 2 p _{ y }^{2}$
Therefore, according to molecular orbital theory, the orbitals involved in bonding are only $\pi$ orbitals $\left(\pi 2 p _{ x }, \pi 2 p _{ y }\right)$.
Since the last $4$ electrons are in the pi molecular orbitals, there are two $\pi$ bonds.