Unknown inorganic compound ' $\mathrm{A}$ ' is used for water softening ' $\mathrm{A}$ ' reacts with $\mathrm{Na}_2 \mathrm{CO}_3$ to generate an alkaline compound 'B' whose $\mathrm{pH}=14$. 'A' on reaction with $\mathrm{CO}_2$ gives cloudy ppt. ' $\mathrm{B}$ ' $+\mathrm{CaO}$ reacts with unknown organic compound ' $\mathrm{C}$ ' to give $\mathrm{C}_6 \mathrm{H}_6$. $\mathrm{A}, \mathrm{B}$ and $\mathrm{C}$, respectively, are

• A

  $\mathrm{Ca}(\mathrm{OH})_2, \mathrm{Na}_2 \mathrm{CO}_3, \mathrm{C}_6 \mathrm{H}_5 \mathrm{COOH}$
• B

  $\mathrm{Ca}(\mathrm{OH})_2, \mathrm{NaOH}, \mathrm{C}_6 \mathrm{H}_5 \mathrm{CH}_2 \mathrm{COOH}$
• Correct answer
  C

  $\mathrm{Ca}(\mathrm{OH})_2, \mathrm{NaOH}, \mathrm{C}_6 \mathrm{H}_5 \mathrm{COOH}$
• D

  $\mathrm{Ca}, \mathrm{NaOH}, \mathrm{C}_6 \mathrm{H}_5 \mathrm{COOH}$

Hence, the correct answer is option: 'C'.