ANS:B - platinum-rhodium

The catalyst typically used in the oxidation of ammonia is platinum-rhodium. Explanation:

1. Catalytic Oxidation of Ammonia: In the oxidation of ammonia to produce nitric oxide (NO), a catalyst is required to facilitate the reaction. This process is a key step in the production of nitric acid, which is an important chemical used in various industries.
2. Platinum-Rhodium Catalyst: The platinum-rhodium catalyst is commonly employed in this reaction due to its effectiveness in promoting the oxidation of ammonia. The presence of both platinum and rhodium in the catalyst composition enhances its catalytic activity and selectivity, ensuring efficient conversion of ammonia to nitric oxide.
3. Role of Catalyst: The catalyst works by providing a surface for the ammonia oxidation reaction to occur at lower temperatures and with increased reaction rates. It helps overcome the activation energy barrier, allowing the reaction to proceed more readily.
4. Other Catalysts: While platinum-rhodium is a widely used catalyst for this application, other catalyst systems may also be employed depending on specific process requirements and conditions. These may include platinum-beryllium, cobalt-molybdenum, or other metal combinations, but platinum-rhodium is particularly favored for its performance in the oxidation of ammonia.