A particle is settling in a liquid under Stokesian conditions. The free falling velocity of the particle is proportional to

ANS:B - particle diameter

Particle diameter refers to the size of a particle, typically measured as the diameter of the smallest sphere enclosing the particle. In the context of particles settling in a liquid, the particle diameter is a crucial parameter that influences various aspects of settling behavior, including settling velocity, sedimentation rate, and resistance to fluid flow. The diameter of a particle is a fundamental characteristic that determines how the particle interacts with the surrounding fluid and the forces acting on it. In Stokesian settling conditions, which occur at low Reynolds numbers, the settling velocity of a spherical particle is directly proportional to the square of its diameter, as described by Stokes' law. Understanding the particle diameter is essential in various fields such as fluid mechanics, environmental engineering, and materials science. It is commonly measured using techniques such as microscopy, laser diffraction, or sieve analysis, depending on the size range and properties of the particles under investigation. In summary, particle diameter refers to the size of a particle, and it plays a critical role in determining its settling behavior and interactions with the surrounding fluid.