The IUPAC name of ${\mathrm{CH}}_3{\mathrm{CH}}_2{\mathrm{OCH}}_2{\mathrm{CH}}_2{\mathrm{CH}}_3$ is

The IUPAC name of ${\mathrm{CH}}_3{\mathrm{CH}}_2{\mathrm{OCH}}_2{\mathrm{CH}}_2{\mathrm{CH}}_3$ is ethoxypropane.

1-ethoxypropane is the designation given to ${\mathrm{CH}}_3{\mathrm{CH}}_2{\mathrm{OCH}}_2{\mathrm{CH}}_2{\mathrm{CH}}_3$ by the IUPAC. Ether, also known as an alkoxy alkane, is what it is.

Hence, correct option is B.