Assumption (c) "Soil particles have different specific gravity" is wrong in the context of sedimentation analysis.

Explanation:
Sedimentation analysis is a method used to determine the particle size distribution of soil samples. It involves allowing soil particles to settle in a suspension and measuring the settling velocity. Based on the settling velocity, the particle size distribution can be inferred using Stokes' law.

Let's discuss each assumption one by one:

a) The assumption that "the soil particles are spherical" is generally valid in sedimentation analysis. This assumption simplifies the calculations and allows for the application of Stokes' law, which assumes spherical particles. In reality, soil particles can have irregular shapes, but for sedimentation analysis purposes, they are considered spherical.

b) The assumption that "particles settle independently of each other and do not affect each other's velocity of settlement" is also generally valid in sedimentation analysis. In dilute suspensions, where the concentration of particles is low, the interaction between particles is minimal, and their settling behavior can be considered independent. However, in concentrated suspensions, particle-particle interactions can occur, resulting in hindered settling or aggregation. These effects are not considered in the basic sedimentation analysis.

c) The assumption that "soil particles have different specific gravity" is incorrect. In sedimentation analysis, it is assumed that all soil particles have the same specific gravity. Specific gravity is the ratio of the density of a substance to the density of a reference substance (usually water). Sedimentation analysis assumes that all particles have the same specific gravity, which simplifies the calculations. In reality, soil particles can have different specific gravities, but this variation is not considered in basic sedimentation analysis.

d) The assumption that "the walls of the jar, in which the suspension is kept, do not affect the settlement" is generally valid in sedimentation analysis. The settling process occurs primarily due to gravity, and the walls of the jar do not significantly affect the settling behavior of the particles. However, it is important to ensure that the jar is clean and smooth to minimize any potential wall effects.

In conclusion, assumption (c) is incorrect in sedimentation analysis as it assumes that all soil particles have the same specific gravity, while in reality, soil particles can have different specific gravities.