Ethanoyl chloride is the IUPAC name of

Ethanoyl chloride is the IUPAC name for acid chloride ${\mathrm{CH}}_3\mathrm{COCl}$. Although acetyl chloride is a more commonly recognised name, it goes by the official IUPAC designation Ethanoyl chloride.

Acetic acid is the source of the acyl chloride known as acetyl chloride (${\mathrm{CH}}_3\mathrm{COCl}$). 

Hence, the correct answer is option (B) ${\mathrm{CH}}_3\mathrm{COCl}$