Question

Which of the following will form the sigma bond?

Answer 1

A sigma bond is a type of covalent bond that is generally formed via axial overlap i.e. overlapping of orbitals along the internuclear axis.

It can be overlap of two $p$ orbitals (axial), two $s$ orbitals, or an $s$ and a $p$ orbital.

All of the above overlappings will lead to the formation of a sigma bond whereas overlapping of two $p$ orbitals (sidewise) will lead to formation of a pi bond.