The reaction, $\mathrm{RX}+\mathrm{R}-\mathrm{ONa}\to \mathrm{R}-\mathrm{O}-\mathrm{R}+\mathrm{NaX}$ is called

Given data: It is given that the reaction, $\mathrm{RX}+\mathrm{R}-\mathrm{ONa}\to \mathrm{R}-\mathrm{O}-\mathrm{R}+\mathrm{NaX}$ is called Williamson's synthesis.

Explanation:

Williamson ether synthesis is an organic reaction that results in the formation of an ether from an organohalide and deprotonated alcohol. Alexander Williamson invented this reaction in 1850. Typically, it involves an SN2 reaction between an alkoxide ion and a primary alkyl halide.

X is Cl, Br, I or another good leaving group. In subsequent examples, we will just use Br, but keep in mind that other halogens work too (except fluorine). So do tosylates and mesylates.

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