Which statement about ethene is correct regarding its carbon–carbon bonds?

• A. It contains a C=C double bond
• B. It contains only C-C single bonds
• C. It contains a C≡C triple bond
• D. It has no carbon–carbon bonds

Answer: (A)

Ethene contains a carbon–carbon double bond. In H2C=CH2 the two carbons share two pairs of electrons: a sigma bond formed by the overlap of sp2-hybridised orbitals and a pi bond formed by sideways overlap of the unhybridised p orbitals. This double bond makes the C=C bond shorter and stronger than a C–C single bond and keeps the molecule planar, with about 120° angles around each carbon, since rotation about a double bond is limited. The other statements don’t fit because there isn’t only a single C–C bond, there isn’t a C≡C triple bond, and there is indeed a carbon–carbon bond in ethene.