Which of the following compounds would you expect to have the least motional modes (translational, rotational, plus vibrational modes)?
a.H2O2
b.H2Se
c.Ne
d.CH3OH
The compound with the least motional modes would be the one with the fewest atoms and least functional groups.
Out of the given compounds, the compound with the least motional modes would be (c) Ne. This is because neon (Ne) is a monatomic gas, meaning it consists of only one atom. It does not have any rotational or vibrational modes since it is a single atom and has no bonds to rotate or vibrate. It only has translational motion, which is the movement of the whole molecule.
The other compounds, H2O2, H2Se, and CH3OH, have multiple atoms and functional groups that can rotate and vibrate. H2O2 and CH3OH have more atoms and functional groups compared to H2Se, so they would have more motional modes.