ANS:A - increased degree of conversion of CO₂ to urea.

An increase in the NH3/CO2 ratio in urea manufacture results in decreased degree of conversion of CO2 to urea. Explanation:

1. Urea Manufacture: Urea is manufactured through the reaction of ammonia (NH3) and carbon dioxide (CO2) in a process known as the urea synthesis.
2. NH3/CO2 Ratio: The NH3/CO2 ratio refers to the molar ratio of ammonia to carbon dioxide used in the urea synthesis process.
3. Conversion of CO2 to Urea: In the urea synthesis reaction, both ammonia and carbon dioxide react to form urea. However, the degree of conversion of CO2 to urea depends on various factors, including the NH3/CO2 ratio.
4. Effect of NH3/CO2 Ratio: An increase in the NH3/CO2 ratio means there is a higher proportion of ammonia relative to carbon dioxide in the reaction mixture. This leads to a situation where there is an excess of ammonia compared to carbon dioxide.
5. Impact on Conversion: With an excess of ammonia, the reaction tends to shift towards the formation of carbamate ions (NH2COO−) rather than urea. As a result, there is a decreased degree of conversion of carbon dioxide to urea under these conditions.
6. Yield of Urea: The decreased conversion of CO2 to urea ultimately leads to a decrease in the overall yield of urea in the process.
7. Specific Volume of Molten Mass: The NH3/CO2 ratio does not directly affect the specific volume of the molten mass in the urea synthesis process. This property is more influenced by factors such as temperature, pressure, and the composition of the reaction mixture.