Classifying organic reaction types in multi-stage synthesis

Steps:

• Analyze reaction 1: CH₃CH₂CH₃ + HI → CH₃CH₂CH₂I + ?, where HI adds to the propane molecule, forming the alkyl iodide product, classifying it as addition.
• Note the ? likely represents H₂ or byproduct, consistent with addition across C-H.
• Analyze reaction 2: CH₃CH₂CH₂I + KOH(aq) → CH₃CH₂CH₂OH + K⁺ + I⁻, where OH⁻ replaces I⁻ via nucleophilic attack, classifying it as substitution.
• Combine types: first addition, then substitution, matching option B.

Why B is correct:

• Addition involves HI adding to propane to form C-I bond; substitution follows SN mechanism per IUPAC, replacing halogen with OH in aqueous base.

Why the others are wrong:

• A: Second reaction is substitution, not elimination (no alkene formed; aq KOH favors SN over E).
• C: First reaction is addition, not elimination (no loss of small molecule like H₂O/HX to form double bond).
• D: First reaction is addition, not substitution (no direct atom replacement without addition step).

Final answer: B