d
\(Pb \left( NO _{3}\right)_{2} \stackrel{\Delta}{\longrightarrow} PbO +\underset{ Brown\, gas (A) }{2 NO _{2}}+\frac{1}{2} O _{2}( g )\)

\(NO _{2}( g )\)\(\xrightarrow \Delta\) \(\begin{array}{*{20}{c}} {{N_2}{O_3}} \\ {\left( B \right)} \end{array}\)

\(N_2 O _{4}+ NO \stackrel{\Delta}{\longrightarrow}\)\(\begin{array}{*{20}{c}} {{N_2}{O_3}} \\ {Blue\,solid\,\left( C \right)} \end{array}\)

\(O.S.\) of nitrogen in \(N _{2} O _{3}\) is +3

\(N _{2} O _{3} 2 x +3(-2)=0\)

\(x=+3\)