Question

number of sigma and pi bond in C2 molecule is

Answer 1

$\bold{\text{number of sigma bond = 0}}$
$\bold{\text{number of pi bond = 2}}$

actually , configuration of C₂ molecule is σ1s² , σ*1s² , σ2s², σ*2s² , π2py² ≈ π2pz²
Here, you see that outermost electrons of C₂ molecule { e.g., π2py² ≈ π2pz²} is 4 . And it belongs to π molecular orbitals . Also you know in bond formation only valance electrons or outermost electrons participate . Hence, in C₂ molecule only π bond exists and number of pi bond = 2


For batter understanding see MO diagram. MO diagram shows that there are two sets of paired electrons in a degenerate pi bonding set of orbitals. Hence, in C₂ molecule only pi bond exists and number of pi bonds = 2

Answer 2

Number of Sigma bonds = 0
Number of Pi bonds = 2
C2 molecule:
Total number of electrons =12
Electronic configuration:

σ1s² , σ*1s² , σ2s², σ*2s² , π2py² ≈ π2pz² 

As we know only valence electrons involve in bonding and they are from 2py and 2pz

Bond order= 1/2(8-4)
=2

C2 is diamagnetic in nature.