1. Formic acid is also an aldehyde. A carboxylic acid has the structure of R-C(O)-OH, while an aldehyde has the formula of R-C(O)H. Formic acid is H-C(O)-OH, where the OH group becomes the R on the aldehyde. So a Tollen's test will give you silver.
2. Take a look at the orbital structure of benzene by itself. All of the unhybridized p orbitals align and overlap. This is a highly stabilized molecular orbital structure with very high electron density. There's a lot of physics behind this, but I hate physics, so I won't go into the details. Some aromatic compounds are electron-withdrawing, i.e. nitrogen containing compounds. The larger nitrogen atom tends to withdraw some of the electron density around the aromatic. The further away the nitrogen atom is, the less deactivated the compound will be. Because of the sp3 hybridization of the methyl group in toluene, it tends to add to the electron density of the ring. Even though some electrons are moving to the substituent, the density still remains around the ring. I guess the simple answer to this would be resonance stabilization, I just took the long route to answer it.
3. If you don't know the explanation for this, try reviewing ortho and para positions in an aromatic ring. You have the right answer though.
4. Again, take a look at ortho/para positions. The carbons that bond to the middle ring on both sides are ortho/para, while the carbons on the middle ring are ipso/meta. The ortho/para are the most reactive, so this is why the end rings are more active.
Hope these answers help. It's hard to explain them without visual aids. If you're still confused, I can try to find/draw some images and upload them.
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Topic: aromatic compounds (Read 3187 times)