JEE Main 2024 · 9 April · evening · Single correct · +4 / −1
The incorrect statement regarding ethyne is
- (a) The carbon - carbon bonds in ethyne is weaker than that in ethene
- (b) Both carbons are sp hybridised
- (c) The C-C bonds in ethyne is shorter than that in ethene
- (d) Ethyne is linear
Answer and solution
Answer (a) The carbon - carbon bonds in ethyne is weaker than that in ethene
Solution
Chemistry ma’am · 3 steps
More bonds between the same two carbons pull them closer and hold them tighter, so ethyne's bond is stronger.
- Hybridisation and shape. Each carbon in HC≡CH has two σ bonds and no lone pairs, so it is sp hybridised. The two sp orbitals point 180° apart, which makes the whole molecule linear.
- Bond order decides. The C≡C bond has one σ and two π bonds, bond order 3. The C=C bond in ethene has bond order 2. More shared electron pairs between the same two nuclei means a shorter and stronger bond.
Statement Data Verdict (a) C≡C weaker than C=C C≡C about 837 kJ mol⁻¹, C=C about 611 kJ mol⁻¹ Incorrect: the triple bond is stronger (b) both carbons sp 2 σ bonds on each C, no lone pairs Correct (c) C≡C shorter than C=C 120 pm against 134 pm Correct (d) ethyne is linear H-C-C angle is 180° Correct - So. The only false statement is (a). The carbon-carbon bond in ethyne is stronger than the one in ethene, not weaker.
The idea to keep. For bonds between the same two atoms, a higher bond order means a shorter and stronger bond: C≡C is shorter and stronger than C=C, which beats C-C.
Answer from the NTA final answer key. Solution by PrepWiser.