The correct answer is: B. For a well graded soil, both uniformity coefficient and coefficient of curvature are nearly unity.
The uniformity coefficient (Cu) is a measure of the range of particle sizes in a soil. It is defined as the ratio of the d60 (the particle size that is 60% finer by weight) to the d10 (the particle size that is 10% finer by weight). The coefficient of curvature (Cc) is a measure of the shape of the particle size distribution curve. It is defined as the square root of the ratio of the d30 (the particle size that is 30% finer by weight) to the d60.
A well-graded soil is a soil that has a uniform distribution of particle sizes. This means that the d60, d10, and d30 are all close to each other. In a well-graded soil, there are no large gaps between the different particle sizes. This makes the soil more stable and less likely to erode.
The uniformity coefficient and coefficient of curvature are both used to determine the grading of a soil. A well-graded soil will have a uniformity coefficient and coefficient of curvature that are both close to unity.
A soil is said to be well graded if it has most of the particles of about the same size. This is not correct because a well-graded soil has a uniform distribution of particle sizes.