GATE 2022 CE (CE1) – Question 59
A wastewater sample contains ammonia at 34 mg NH₃/L and nitrate at 6.2 mg NO₃⁻/L. Atomic weights: N=14, H=1, O=16 g/mol. Find total nitrogen (mg N/L, one decimal).
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Correct answer: 29.25 to 29.55
Explanation
Convert each species to its nitrogen mass. Ammonia contributes $34(14/17)=28$ mg N/L; nitrate contributes $6.2(14/62)=1.4$ mg N/L.
Adding the nitrogen contributions gives **29.4 mg N/L**. Hydrogen and oxygen mass must not be counted as nitrogen.