The correct answer is D. Sulphur.
Ethyl mercaptan is a chemical compound with the formula C2H5SH. It is a colourless liquid with a strong, unpleasant odour. It is used as a warning agent in natural gas and liquefied petroleum gas (LPG) to make leaks easily detectable.
Ethyl mercaptan is a mercaptan, which is a compound that contains a mercaptan group, -SH. Mercaptans are typically foul-smelling, and are used as odorants in natural gas and LPG to make leaks easily detectable.
The other options are incorrect because they are not elements that are found in ethyl mercaptan. Bromine, fluorine, and chlorine are all halogens, which are elements that are highly reactive and do not occur naturally in the free state.