Which of the following conditions will most likely promote an $E2$ reaction with an alkyl halide?

• A. A polar protic solvent with no added base
• B. A strong base such as $\mathrm{NaOEt}$ in ethanol
• C. A weak base such as $H_{2}O$ in water
• D. A strong acid such as $H\mathrm{Br}$

Answer: (B)

Verified step by step guidance

1. Understand that an E2 reaction is a bimolecular elimination that requires a strong base to abstract a proton while the leaving group departs simultaneously.
2. Recognize that polar protic solvents can stabilize ions but do not necessarily promote E2 unless a strong base is present; without a base, elimination is unlikely.
3. Identify that a strong base such as sodium ethoxide (NaOEt) in ethanol provides the necessary conditions for E2 by both deprotonating the β-hydrogen and facilitating the elimination.
4. Note that weak bases like water (H2O) are generally poor at abstracting protons and thus favor substitution or no reaction rather than E2 elimination.
5. Understand that strong acids like HBr tend to protonate the substrate or favor substitution reactions rather than promoting E2 elimination.