A compound which is a byproduct of the chloralkali process is NaOH. Hence compound B is NaOH.
When NaOH is treated with acidic oxide neutralization process occurs. For example, If NaOH is treated with carbon-di-oxide, it gives Sodium carbonate.
2NaOH + CO2 → Na2CO3 + H2O
When electricity is passed through an aqueous solution of sodium chloride it decomposes to form sodium hydroxide. The process is called the chlor-alkali alkali process.
An aqueous solution of sodium chloride is called brine.
2NaCl (aq) + 2H2O(l) (electrolysis) → 2NaOH(aq) + Cl2(g) + H2(g).