Halogen compounds — common mistakes

When asked to explain the low reactivity of halogenoarenes, you must mention the overlap of the halogen's p-orbital with the ring's $\pi$-system leading to a C-X bond with 'partial double bond character'. Simply stating 'the bond is stronger' is not enough for full marks; you must explain why it is stronger.

Ethanol is a less polar solvent than water. This makes the hydroxide ion ($OH^-$) less well-solvated and therefore a stronger base. A stronger base is more likely to remove a proton (elimination) than to attack a carbon atom (substitution). Additionally, high temperature provides the activation energy needed for elimination.

Yes, very. In (chloromethyl)benzene ($C_6H_5CH_2Cl$), the chlorine atom is attached to a carbon that is not part of the benzene ring. This C-Cl bond behaves like a typical primary halogenoalkane bond. It is not strengthened by p-orbital overlap and will readily undergo nucleophilic substitution.

Replacements include hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs). HCFCs still contain chlorine but are less stable and break down in the lower atmosphere, having a smaller effect on the ozone layer. HFCs contain no chlorine and have zero ozone depletion potential, but they are potent greenhouse gases, so their use is also being phased down.