Q1: Hazin's formula is used for the settlement velocity of the particles of diameter

ANS:D - greater than 0.1 mm.

Hazen's formula, also known as Hazen-Williams formula, is not used for calculating the settling velocity of particles. Instead, it is a hydraulic formula commonly used to calculate the flow rate of water in pressurized pipes, such as those used in water distribution systems. For calculating the settling velocity of particles, Stokes' law is typically used. Stokes' law applies to particles in a fluid medium, and it calculates the settling velocity based on the particle size, density, fluid viscosity, and gravitational acceleration. However, if we were to discuss particle sizes in the context of sedimentation or settling processes, particles with diameters less than 0.01 mm (millimeters) are typically classified as clay-sized particles. These particles are very fine and can remain suspended in water for extended periods. Therefore, if we were to relate Hazen's formula to particle sizes, it would not be appropriate to specify a particle diameter.