Based on the compounds given, I can say that the substance that is considered essential in the plastic making is NITRIC ACID. This substance is also known as aqua fortis and spirit of niter wherein this decomposes into oxides of nitrogen and water. The answer would be the last option. Hope this helps.
Nitric acid is a corrosive liquid inorganic acid HNO3 used mostly as an oxidizing agent, and in making organic compounds.
<em><u>Nitric acid is used in the production of ammonium nitrate for fertilizers, making plastics, and in the manufacture of dyes.</u></em> It is also used for making explosives such as nitroglycerin and TNT.
