NCERT Exercise 4.29 - Chemical Bonding and Molecular Structure

Question: With x as internuclear axis, which overlap will not form a sigma bond: 1s-1s, 1s-2px, 2py-2py, or 1s-2s?

Answer: 2py-2py will not form a sigma bond along the x-axis; it gives sidewise overlap, hence a pi bond.

Full step-by-step NCERT solution with diagrams on Something by Zero.