Sodium hydroxide (NaOH) is commonly used base and is hygroscopic, that is, it absorbs moisture from the atmosphere and becomes sticky.
Thus, base B is NaOH (sodium hydroxide). It is also a by-product of chlor-alkali process, The acidic oxide reacts with base to give salt and water.
If CO2 is the acidic oxide taken, then the following reaction takes place with 'B'.
2NaOHSodium hydroxide (B)+CO2⟶+2Na2CO3Sodium carbonate+H2O
Such a reaction is called a neutralisation reaction.