The ratio of the difference between the void ratio of the soil in its loosest state and its natural void ratio (e) to the difference between the void ratios in the loosest and fully dense state, is generally termed as

ANS:D - all the above.

1. Degree of density: While "degree of density" may seem like a reasonable term, it is not commonly used in soil mechanics to describe the specific ratio mentioned in the question. The term "degree of density" could refer to various measures of soil density, but it doesn't specifically denote the ratio described.
2. Relativity: "Relativity" is a concept in physics that refers to the relationship between different observers' measurements of the same event. In the context of soil mechanics, "relativity" doesn't directly relate to the ratio between void ratios as described in the question.
3. Density index: The density index is a term commonly used in soil mechanics to describe the ratio of the difference between the void ratio of the soil in its loosest state and its natural void ratio to the difference between the void ratios in the loosest and fully dense state. It is a measure of the relative density or compactness of soil and is widely recognized and used in geotechnical engineering.