According to VBT any covalent bond will be formed by overlapping of atomic orbitals of bonded atoms provided atomic orbitals must be half-filled and electrons be in opposite spin. According to type of overlapping covalent bonds can be classified as (a)` sigma`-bond (b) `pi`-bond (c ) `delta`-bond :
The combination of orbital that can not produce non-bonding molecular orbital is (internuclear axis is z-axis ) :