Final answer:
The molecule C2H4 (ethene) has a carbon atom with a trigonal planar distribution of electron density due to one double bond and two single carbon-hydrogen bonds around each carbon atom.
Step-by-step explanation:
The question asks about the distribution of electron density around a carbon atom in various molecules, specifically looking for a molecule where the carbon atom displays a trigonal planar shape. To determine this, we should consider the bonding and electron-pair geometry of the carbon atoms in each molecule option provided.
Looking at ethene (C2H4), which is option b, we see that it has a double bond between the carbon atoms. This double bond counts as one region of electron density, while the two single bonds to hydrogen on each carbon count as the other regions. Thus, ethene's carbon atoms each have three regions of electron density and no lone pairs, fitting the criteria for a trigonal planar distribution of electron density around the carbon atom.
Therefore, the correct answer is b. C2H4, where the geometry around each carbon in the molecule is trigonal planar with bond angles close to 120°.