Q.Which bond is stronger σ or π? Why?

Step 1. Bond strength depends directly on the EXTENT of orbital overlap (VB theory's third salient feature, section 10.7.1) — the greater the overlap, the more energy is released on bond formation, and the stronger the resulting bond.

Step 2. A σ bond forms by HEAD-ON (axial) overlap, directly along the internuclear axis — the two orbital lobes point straight at each other, maximising the overlap region.

Step 3. A π bond forms by SIDEWAYS (lateral) overlap of two orbitals lying parallel to, but offset from, the internuclear axis — this geometry gives a smaller, less effective region of overlap than a head-on approach. …

Connect the overlap-geometry difference between σ (axial) and π (lateral) bonds directly …

• Reasoning purely from bond-energy TABLES (e.g. comparing a C-C single bond's energy to 'half' of a C=C double bond's energy) rather than from the underlying overlap-geometry argument the question is testing. …