$1.$ Explore the environmental and agronomic implications of the widespread use of synthetic ammonia in agriculture, including its role in enhancing crop yield versus its contribution to nitrogen pollution in water bodies.

$2.$ Delve into the global nitrogen cycle, focusing on the role of industrial processes like the Haber$-$Bosch process for synthetic ammonia production, and how these processes have altered the natural nitrogen balance.

$3.$ Investigate the chemical properties of nitric acid that make it a crucial intermediate in the manufacture of various nitrogen fertilizers, and discuss the environmental safety measures needed during its production and transportation.

$4.$ Analyze the benefits of using urea as a high$-$nitrogen fertilizer compared to other nitrogen sources, including its economic viability, efficiency in various soil types, and the potential for volatilization and leaching.