A dry pellet of a common base $B$, when kept in open absorbs moisture and turns sticky. The compound is also a by-product of the chloralkali process. What type of reaction occurs when $B$ is treated with an acidic oxide?

The correct option is B Neutralization reaction
The acidic oxides react with a base to give salt and water. Sodium hydroxide reacts with protic acids to produce water and the corresponding salts.

For example, when sodium hydroxide reacts with $HCl,NaCl$ salt and water is formed.

Hence the reaction is neutralization reaction due to a formation of salt and water.

$NaOH+HCl\to H_{2}O+NaCl$