ANS:B - 190°C and 200 atm.

In the urea manufacturing process, the urea autoclave is a crucial component where urea synthesis takes place under high temperature and pressure conditions. The autoclave provides the necessary environment for the urea reaction to occur efficiently. The specified temperature of 190°C and pressure of 200 atm in the autoclave are optimal for urea synthesis. Here's an explanation of these conditions:

1. Temperature (190°C): This temperature is sufficiently high to facilitate the reaction between ammonia (NH3) and carbon dioxide (CO2) to form ammonium carbamate (NH2COONH2), which is an intermediate compound in the urea synthesis process. The elevated temperature helps overcome the activation energy barrier for the reaction to proceed at a reasonable rate.
2. Pressure (200 atm): The high pressure in the autoclave helps maintain the ammonia and carbon dioxide in the liquid phase, which is crucial for their effective dissolution and reaction. Additionally, the high pressure favors the conversion of ammonium carbamate into urea, as it stabilizes the intermediate and drives the reaction towards urea formation.

Overall, the combination of high temperature and pressure in the urea autoclave ensures efficient urea synthesis, leading to higher yields of urea production. These conditions are carefully controlled to optimize the process while ensuring safety and stability within the equipment.