Answer: B) carbon + oxygen -- carbon dioxide
Explanation: The symmetry of a carbon dioxide molecule is linear and centrosymmetric at its equilibrium geometry. The length of the carbon-oxygen bond in carbon dioxide is 116.3 pm, noticeably shorter than the roughly 140-pm length of a typical single C–O bond, and shorter than most other C–O multiply-bonded functional groups such as carbonyls. Since it is centrosymmetric, the molecule has no electric dipole moment. As a linear triatomic molecule, CO2 has four vibrational modes as shown in the diagram. In the symmetric and the antisymmetric stretching modes, the atoms move along the axis of the molecule. There are two bending modes, which are degenerate, meaning that they have the same frequency and same energy, because of the symmetry of the molecule. When a molecule touches a surface or touches another molecule, the two bending modes can differ in frequency because the interaction is different for the two modes. Some of the vibrational modes are observed in the infrared (IR) spectrum: the antisymmetric stretching mode at wavenumber 2349 cm−1 (wavelength 4.25 μm) and the degenerate pair of bending modes at 667 cm−1 (wavelength 15 μm). The symmetric stretching mode does not create an electric dipole so is not observed in IR spectroscopy, but it is detected in by Raman spectroscopy at 1388 cm−1 (wavelength 7.2 μm).