C$.(5$ pts$).$ For the bimolecular reaction $A+BAB,$ the diffusion constant, $D$ in $k_{on}=4DR,$ is replaced

by $D_A+D_B$ if both species are mobile. If A and $B$ are viewed as hard spheres of radius $R_s,$ establish that

$k_{on}=8k_B\frac{T}{3}$ in the diffusion model. Of note, $k_B=$ Boltzmann constant, $T=$ absolute temperature, and $=$

viscosity.