Question

Numbers of $\sigma$ and $pi$ bonds in $C_2$ molecule is/are:

• A. $1\sigma$ and $1\pi$
• B. $1\sigma$ and $2\pi$
• C. $2\pi$ only
• D. $1\sigma$ and $3\pi$

Answer 1

Answer: (C)

$2\pi$ only

Configuration of $C₂$ molecule is $\sigma 1s²,\sigma \ast 1s²,\sigma 2s²,\sigma \ast 2s²,\pi 2py²\approx \pi 2pz²$

Here, you see that outermost electrons of $C₂$ molecule { e.g., $\pi 2py²\approx \pi 2pz²$} is $4$ . And it belongs to $\pi$ molecular orbitals. Also, you know in bond formation only valence electrons or outermost electrons participate. Hence, in $C₂$ molecule only $\pi$ bond exists and number of pi bond = $2$

Conclusion: hence the answer option(C) is correct.