Considering x-axis as the internuclear axis which out of the following will not form a sigma bond and why? (a) 1s and 1s (b) 1s and `2p_(x)` (c) `2p_(y)` and `2p_(y)` (d) 1s and 2s.

Explanation

(a), (b) and (d) will form sigma bonds because s-orbitals are spherically symmetric. (c), i.e., 2p, and `2p_y` cannot form a sigma bond because being along Y-axis, they cannot overlap axially (head on). They can only overlap sidewise to form a pi bond if X-axis is the internuclear axis.