84: The correct answer is B. If you look at the symmetry of that molecule, there are 12 Hydrogens that are identical (all of the secondary carbons have two Hydrogens). There are also two hydrogens that, again, are identical due to symmetry (the hydrogen off each of the two tertiary carbons). You don't even need to factor in peak-splitting to get this problem right, because none of the other molecules will give a 12 H to 2 H ratio.
86: This is one of the handful of of the opted problems where the answer key is wrong. In pyridine, you have three pi bonds and six pi electrons (this compound is also aromatic). The lone pair on the Nitrogen is not involved in the pi bonding at all (or the aromaticity). Molecular Orbital Theory will show that this compound (which basically acts like Benzene with respect to pi bonding) will have three occupied pi molecular orbitals (so the answer to this problem should be three). One pi molecular orbital (at the lowest energy level) will have one node, and the next two (at equal energy levels to each other) will have two nodes, although that is not relevant with respect to the OAT.
98: The first step of this reaction (addition of thionyl chloride to benzoic acid) will form an acid chloride (the carbon off the benzene ring is double-bonded to an oxygen and is single-bonded to a chlorine). In the second step of this reaction, the hydroxyl group of the ethanol displaces the chlorine and also loses it's own Hydrogen, forming the ester shown in answer choice B.
