Diffusivity of liquids refers to the ability of a liquid to mix or spread out into another liquid or gas. It is an important parameter in various chemical engineering processes such as distillation, absorption, and extraction. There are several equations that can be used to determine the diffusivity of liquids, but the correct answer for this question is option 'B', the Wilke-Chan equation.

The Wilke-Chan equation is used to calculate the diffusion coefficient or diffusivity of a liquid mixture. It is an extension of the Wilke-Lee equation, which is also commonly used in chemical engineering. The Wilke-Chan equation takes into account the effect of molecular size and shape on the diffusivity of liquids.

The equation is given as follows:

D12 = (X1/X2) * (D1 + D2) / (X1/D1 + X2/D2)

Where:
- D12 is the diffusivity of component 1 in the presence of component 2.
- X1 and X2 are the mole fractions of components 1 and 2, respectively.
- D1 and D2 are the diffusivities of components 1 and 2, respectively.

The equation considers the diffusivities of each component individually as well as the mole fractions of the components in the mixture. It accounts for the fact that different components may have different diffusivities and that the diffusivity of a component may be influenced by the presence of other components.

The Wilke-Chan equation is particularly useful when dealing with mixtures of liquids with different molecular sizes and shapes. It provides a more accurate estimation of the diffusivity compared to other equations that do not consider these factors.

In summary, the diffusivity of liquids can be determined using the Wilke-Chan equation, which takes into account the molecular size and shape of the components in the mixture. This equation provides a more accurate estimation of diffusivity compared to other equations and is commonly used in chemical engineering.