Among the given options, urea (Option 1) contains the maximum percentage of nitrogen by mass. Nitrogen is an essential element for plant growth and is commonly found in fertilizers.
Option 2, ammonium cyanide, is not as nitrogen-rich compared to urea. It is a toxic compound used in the production of pharmaceuticals and dyes.
Option 3, ammonium carbonate, contains less nitrogen compared to urea. It is commonly used as a leavening agent in baking and in the production of certain chemicals.
Option 4, ammonium nitrate, contains nitrogen but in a lower percentage than urea. It is commonly used as a fertilizer and in the production of explosives.
Urea, on the other hand, has the highest percentage of nitrogen by mass among the given options. It is widely used as a nitrogen fertilizer in agriculture. However, it is important to note that the percentage of nitrogen in urea may vary depending on the specific product or formulation.