have 50% s character and 50% p character.13 . B
A resonance structure describes an arrangement of electrons in a molecule. Different resonance
structures can be derived by moving electrons in unhybridized p-orbitals throughout a molecule
containing conjugated bonds. In molecules that contain multiple resonance structures, some are
usually more stable than others; however, each resonance structure is not necessarily the most
common form a molecule takes, eliminating statement III. Statement I has reversed the
terminology for resonance structures: the electron density in a molecule is the weighted average
of all possible resonance structures, not the other way around.
14 . D
An electron in the n = 4 shell and the l = 2 subshell can have five different values for ml: –2, –1, 0, 1,
or 2. In each of these orbitals, electrons can have positive or negative spin. Thus, there are 5 × 2 =
10 possible combinations of quantum numbers for this electron.
15 . D
π bonds do not permit free rotation, unlike σ bonds; this makes triple bonds more rigid than
single bonds. Triple bonds are stronger and shorter bonds than single bonds, eliminating choices
(A) and (B). Both single and triple bonds contain one σ bond, eliminating choice (C).