Which of the following oxides is amphoteric? MCQ with Answer and Explanation

Explanation:
A small amount of ethanol (alcohol) is added to chloroform to inhibit its oxidation by air to toxic phosgene (COCl₂) and HCl. Ethanol acts as a negative catalyst (stabilizer) by consuming any formed phosgene. MnO₂, Pt, Fe are positive catalysts. Negative catalysts are also called inhibitors, used to prevent undesirable reactions.

Explanation:
Baking powder contains sodium bicarbonate (NaHCO₃) and a weak solid acid such as tartaric acid or cream of tartar (potassium hydrogen tartrate). When moistened, they react to produce CO₂, making dough rise. Baking soda alone requires an acidic ingredient (yogurt, lemon). The acid in baking powder ensures reliable leavening. Sodium chloride and calcium carbonate do not serve this purpose.

Explanation:
PVC (polyvinyl chloride) is an addition polymer of vinyl chloride monomer (CH₂=CHCl). It is used for pipes, cables, flooring, and medical equipment. Teflon from tetrafluoroethene, polythene from ethylene, nylon is a polyamide (condensation polymer). PVC can be rigid or flexible depending on plasticizers added. It is a thermoplastic. Disposal of PVC by burning produces toxic HCl gas.