The reaction, ${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{ONa}+{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{I}\to {\mathrm{C}}_2{\mathrm{H}}_5{\mathrm{OC}}_2{\mathrm{H}}_5+\mathrm{NaI}$, is called

Given data : It is given to identify the reaction  ${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{ONa}+{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{I}\to {\mathrm{C}}_2{\mathrm{H}}_5{\mathrm{OC}}_2{\mathrm{H}}_5+\mathrm{NaI}$

Explanation 
We need to find that the above reaction is called from the given options.
Williamson Synthesis – Alkyl halide is heated in the presence of sodium or potassium alkoxides. This process is used to create ethers, such as
${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{ONa}+{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{I}⟶{\mathrm{C}}_2{\mathrm{H}}_5-{\mathrm{OC}}_2{\mathrm{H}}_5+\mathrm{NaI}$

Hence, the correct option (B). Williamson's reaction.