Correct Answer - Option 2 : 0.5 mm

**Darcy’s law:**

The flow of free water through soil is governed by Darcy’s law. Darcy demonstrated experimentally that for laminar flow in a homogeneous soil, the velocity of flow (v) is given by

V = ki

Where

k = coefficient of permeability, i = hydraulic gradient

The velocity of flow is also known as the discharge velocity or the superficial velocity.

Using Allen Hazen’s equation for velocity, it can be shown that the maximum diameter of the particle for the flow to be laminar is about 0.50 mm.