Quy trình sản xuất \({\rm{HN}}{{\rm{O}}_3}\) trong công nghiệp từ nguyên liệu \({\rm{N}}{{\rm{H}}_3}\) được thực hiện như sau:

\({\mathop{\rm BTNT}\nolimits} ({\rm{N}})\) ta có \({{\rm{n}}_{{\rm{N}}{{\rm{H}}_3}}} = {{\rm{n}}_{{\rm{HN}}{{\rm{O}}_3}}} = 2\,\,(\;{\rm{mol}})\)

 4NH3+5O2→Pt,t°4NO+6H2O2      →          2,5                                       2                            mol

\(\begin{array}{l}2{\rm{NO}} + {{\rm{O}}_2} \to 2{\rm{N}}{{\rm{O}}_2}\\2\,\,\,\,\, \to \,\,\,\,1\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,2\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,mol\end{array}\)

\(\begin{array}{l}4{\rm{N}}{{\rm{O}}_2} + {{\rm{O}}_2} + 2{{\rm{H}}_2}{\rm{O}} \to 4{\rm{HN}}{{\rm{O}}_3}\\2\,\,\,\, \to \,\,\,\,\,0,5\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,mol\end{array}\)

\({n_{{O_2}}}\)ban đầu = a – 2 (mol)

Chọn C.