• # question_answer In a gaseous phase reaction, ${{A}_{2}}(g)\,\xrightarrow{\,}\,B(g)\,+\frac{1}{2}\,(g),$ the increase in pressure from 100 mm to 120 mm is noticed in 5 min. The rate of disappearance of ${{A}_{2}}$ in mm ${{\min }^{-1}}$ is A) 4                                  B) 8    C) 16                                 D) 2

 ${{A}_{2}}(g)\xrightarrow{\,}\,B(g)+\frac{1}{2}\,C(g)$ $-\frac{d[{{A}_{2}}]}{dt}=2\,\frac{d\,[C]}{dt}$ $\frac{d\,[C]}{dt}=2\,\frac{120-100}{5}=4\,\,mm\,\,{{\min }^{-1}}$ $\therefore$      $\frac{d\,[{{A}_{2}}]}{dt}=2\times 4$ $=8\,\,mm\,{{\min }^{-1}}$