Which of the following is an exothermic reaction?

The reactions in which a large amount of heat is produced along the products are known as exothermic reactions. 

Dissolution of sodium hydroxide in water releases a large amount of heat so it is an exothermic reaction. Other reactions absorb heat during the reaction so they are known as endothermic reactions. Its reaction is given as
$\mathit{NaOH}\left(s\right)+H_{2}O\left(l\right)\to \mathit{ N}{a^{+}}^{ }\left(\mathit{aq}\right)+O{H}^{-}\left(\mathit{aq}\right)+\mathit{Heat}$