ANS:E - shape, size and weight of grain.

1. Shape of the grain: The shape of the grain can affect its settling velocity to some extent. Irregularly shaped grains may experience more resistance from the surrounding fluid compared to smoother, spherical grains. However, the influence of shape on settling velocity is typically secondary to other factors like size and weight.
2. Size of the grain: The size of the grain is a critical factor affecting settling velocity according to Stokes's law. Larger grains experience greater resistance from the surrounding fluid and settle more quickly than smaller grains. The settling velocity is directly proportional to the square of the particle's radius (or diameter), meaning that small changes in particle size can significantly affect settling behavior.
3. Weight of the grain: The weight, or mass, of the grain also influences its settling velocity. Heavier grains settle more quickly than lighter grains of the same size and shape. The settling velocity is directly proportional to the density difference between the particle and the fluid medium.

While all three factors—shape, size, and weight—contribute to the settling behavior of grains, the size of the grain is typically the most influential factor according to Stokes's law. However, in practical applications, engineers and scientists consider all three factors when analyzing sediment transport, particle settling, and related phenomena in fluid dynamics and sedimentology.