Correct Answer: Brine
Subject: 2025
Explanation: <b>Key Fact</b><br>A saturated or concentrated aqueous solution of sodium chloride ($NaCl$) is known as brine. The chlor-alkali process involves the electrolysis of brine to produce chlorine gas, hydrogen gas, and sodium hydroxide.<br><br><b>Additional Info</b><br>Topic: Salts and Industrial Chemicals.<br><br><b>Why the other options are wrong</b><br>Option A: Antacids are mild bases like $Mg(OH)_2$ or $NaHCO_3$ used to neutralize stomach acid.<br>Option B: Caustic soda is sodium hydroxide ($NaOH$).<br>Option C: Correct.<br>Option D: Baking soda is sodium hydrogen carbonate ($NaHCO_3$).<br><br><b>Exam Trick</b><br>Electrolysis of brine ($NaCl + H_2O$) = Chlor-alkali process.<br><br><b>Final Answer</b><br>Option C — Brine.