Step 1: Concept
This sequence involves the basic hydrolysis of an ester (saponification) followed by acidification of the resulting salt.
Step 2: Meaning
Esters react with bases to form a salt of the carboxylic acid and an alcohol. Acidification of the carboxylate salt restores the parent carboxylic acid.
Step 3: Analysis
1. $\text{CH}_3\text{CH}_2\text{COOCH}_3$ (Methylpropanoate) reacts with NaOH to form $\text{CH}_3\text{CH}_2\text{COONa}$ (Sodium propanoate, A) and methanol.
2. $\text{CH}_3\text{CH}_2\text{COONa}$ (A) reacts with HCl to form $\text{CH}_3\text{CH}_2\text{COOH}$ (Propanoic acid, B) and NaCl.
Step 4: Conclusion
The final product B is propanoic acid.
Final Answer: (D)