ANS:A - kinematic viscosity

The dimension of mass diffusivity is the same as that of kinematic viscosity. Mass diffusivity (𝐷D) is a measure of the rate at which mass diffuses through a medium. It is defined as the ratio of the molecular diffusivity (𝐷𝑚Dm​) to the density of the medium (𝜌ρ): 𝐷=𝐷𝑚𝜌D=ρDm​​ The dimension of mass diffusivity (𝐷D) is given by: [𝐷]=[𝐷𝑚][𝜌]=𝐿2𝑇×𝐿3𝑀=𝐿2𝑇[D]=[ρ][Dm​]​=TL2​×ML3​=TL2​ Kinematic viscosity (𝜈ν) is defined as the ratio of dynamic viscosity (𝜇μ) to density (𝜌ρ): 𝜈=𝜇𝜌ν=ρμ​ The dimension of kinematic viscosity (𝜈ν) is given by: [𝜈]=[𝜇][𝜌]=𝑀𝐿⋅𝑇×𝐿3𝑀=𝐿2𝑇[ν]=[ρ][μ]​=L⋅TM​×ML3​=TL2​ Therefore, the dimension of mass diffusivity ([𝐷][D]) and kinematic viscosity ([𝜈][ν]) are the same, both being 𝐿2/𝑇L2/T.