Acid-base neutralization forming carboxylate salt without gas

Steps:

• Propanoic acid (CH3CH2COOH) reacts with X to yield sodium propanoate (CH3CH2COONa), indicating salt formation via deprotonation.
• No gas evolution rules out reactions producing CO2, like those with carbonates or bicarbonates.
• Room temperature suggests a straightforward neutralization, not requiring heat.
• X must be a sodium-containing base that fully neutralizes the acid without side products.

Why B is correct:

• NaOH(aq) reacts with carboxylic acids to form the sodium carboxylate and water: CH3CH2COOH + NaOH → CH3CH2COONa + H2O, per acid-base neutralization definition.

Why the others are wrong:

• A: NaHCO3(aq) produces CO2 gas: CH3CH2COOH + NaHCO3 → CH3CH2COONa + H2O + CO2.
• C: Na2CO3(aq) produces CO2 gas: 2CH3CH2COOH + Na2CO3 → 2CH3CH2COONa + H2O + CO2.
• D: Na2SO4(aq) is a neutral salt and does not react with the acid to form the carboxylate.

Final answer: B