Which one among the following nitrogen compounds has the least percentage of nitrogen by mass?

To determine the least percentage of nitrogen by mass, we calculate the mass percent for each compound using the formula: (Total mass of Nitrogen / Molar mass of compound) × 100. Ammonia (NH3) has the highest nitrogen content at approximately 82.35%. Ammonium nitrate (NH4NO3) contains about 35% nitrogen. Ammonium hydroxide (NH4OH), with a molar mass of approximately 35 g/mol and one nitrogen atom (14 g/mol), contains roughly 40% nitrogen. In contrast, ammonium phosphate ((NH4)3PO4) has a much higher molar mass (approximately 149 g/mol) due to the heavy phosphate group (PO4). Although it contains three nitrogen atoms (42 g/mol), the calculation (42/149 × 100) yields approximately 28.2% nitrogen. Therefore, ammonium phosphate has the lowest percentage of nitrogen by mass among the given options.