Which atoms in a toluene molecule always remain in the same plane and why? (2) Which atoms in a propyne molecule remain in a straight line and why?

Explanation

An `sp^(2)` - hybridised carbon atom and the atoms directly attached to it always remain in the same plane. Therefore, in toluene , all the atoms except 3 H-atoms of methly group (i.e, seven C - and five H - atoms) remain in the same plane.
(2) An sp - hybridised carbon atom and the atoms directly attached to it remain in a straight line. Therefore, in propyne molecule `(CH_(3)-C-=CH)`, all the atoms except the 3 hydrogen atoms of methyl group remain in the same strainght line.