Nucleophilic reactions of bromomethane (CH₃Br)

Steps:

• Statement 1: Aqueous NaOH promotes SN2 substitution; CH₃Br + OH⁻ → CH₃OH (methanol), not ethanol (C₂H₅OH), so false.
• Statement 2: Ethanolic NaOH favors elimination, but CH₃Br lacks β-hydrogen, preventing E2 to ethene (C₂H₄); instead, SN2 to CH₃OH occurs, so false.
• Statement 3: Ethanolic KCN enables SN2 substitution; CH₃Br + CN⁻ → CH₃CN (ethanenitrile), so true.
• Only statement 3 is correct, matching option B (statement 3 only).

Why B is correct:

• B identifies the sole accurate reaction, aligning with SN2 mechanism for primary alkyl halides where CN⁻ replaces Br⁻ without elimination.

Why the others are wrong:

• A includes statement 1, but product is methanol, not ethanol.
• C includes statement 2, but no β-hydrogen for ethene formation.
• D includes all, but statements 1 and 2 are incorrect.

Final answer: B