Consider the following reaction: $2 NO_{2(g)} + F_{2(g)} \longrightarrow 2 NO_2F_{(g)}$. The expression for the rate of reaction in terms of the rate of change of partial pressure of reactant and product is/are:

• A
  rate $= -\frac{1}{2} \left[ \frac{dp(NO_2)}{dt} \right]$
• B
  rate $= \frac{1}{2} \left[ \frac{dp(NO_2)}{dt} \right]$
• C
  rate $= -\frac{1}{2} \left[ \frac{dp(NO_2F)}{dt} \right]$
• D
  rate $= \frac{1}{2} \left[ \frac{dp(NO_2F)}{dt} \right]$