Lower temperature and large excess of ammonia in urea melt

ANS:B - decreases biuret formation

Lower temperature and a large excess of ammonia in urea melt decrease biuret formation. Biuret is a urea derivative that forms when urea is heated at high temperatures or when exposed to excess ammonia. However, at lower temperatures and in the presence of a large excess of ammonia, the likelihood of biuret formation decreases. This is because lower temperatures slow down the reaction kinetics, reducing the extent of biuret formation. Additionally, excess ammonia helps to minimize the formation of biuret by effectively diluting the urea and providing more favorable reaction conditions for the desired reactions. Therefore, under such conditions, the formation of biuret is minimized, which is desirable because biuret is considered an impurity in urea and can reduce its quality and effectiveness as a fertilizer.