Which orbitals form a pi bond

Answer: p orbitals

Explanation: pi bonds are formed by side ways overlap of p orbital which leads lower energy state.

If we have p orbital in adjacent carbons then they will undergoes sideways overlap to form pi bond.

For example, Ethene, CH2=CH2 has p orbitals on adjacent carbons which combine sideways and result a double bond (called pi bond)

Single covalent bonds that form between nuclei are created from the "head-to-head" overlap of orbitals and are called sigma (s) bonds