Final answer:
KOH (Potassium hydroxide) is the compound that could serve as a reactant in a neutralization reaction, as it is a strong base capable of reacting with an acid to form water and a salt.
Step-by-step explanation:
The compound that could serve as a reactant in a neutralization reaction is KOH (Potassium hydroxide), which is a strong base. In a neutralization reaction, an acid and a base react to form water and a salt. Neutralization reactions involve the combination of H+ ions from the acid and OH- ions from the base to produce water. NaCl is a salt and CH₃OH (methanol) and CH₃CHO (acetaldehyde) are neither strong acids nor bases and hence, do not typically participate in neutralization reactions.
For buffer solutions, certain combinations of acids and bases or their respective salts can create a solution that resists changes in pH upon the addition of small amounts of acid or base. Notable combinations that can create buffer solutions are H3PO4 and NaH₂PO4, and NH3 and (NH4)3PO4. NaHCO3 and NaCl, and NaOH and NaCl do not form buffer solutions as they do not consist of a weak acid or base paired with its conjugate.