Q$3.$ In a gas mixture of Gas A and Gas $B,$ steady$-$state equimolar counter diffusion is occuring at a total pressure of $78$kPa and temperature of $24C.$ If the partial pressure of Gas B at two places $2cm$ apart and perpendicular to the direction of diffusion are $12$kPa and $2$ kPa respectively, and the mass diffusion flux of oxygen in the mixture is $1,68{10}^{-5}$kgmo$\frac{l}{m^2}s.$ Please calculate the molecular diffusivity for the system.