In the hydrolysis reaction of butyl chloride,the concentration of reactant at $600 \ s$ is determined using a tangent at $t_2 = 800 \ s$ and $t_1 = 400 \ s$. Given the concentrations $[R_2] = 0.0165 \ mol \ L^{-1}$ and $[R_1] = 0.037 \ mol \ L^{-1}$,calculate the instantaneous rate $r_{ins}$ at $600 \ s$.

• A
  $5.125 \times 10^{-5} \ mol \ L^{-1} \ s^{-1}$
• B
  $2.562 \times 10^{-5} \ mol \ L^{-1} \ s^{-1}$
• C
  $1.025 \times 10^{-4} \ mol \ L^{-1} \ s^{-1}$
• D
  $5.125 \times 10^{-4} \ mol \ L^{-1} \ s^{-1}$