ANS:E - All the above.

1. A maximum value of dry density is obtained at optimum water content. - This statement is generally correct. The maximum dry density is typically achieved at the optimum water content during compaction.
2. At low value of water content most soils tend to be stiff. - This statement is generally true. At low water contents, soils tend to be drier and stiffer, which may affect their engineering properties.
3. At high water content, the dry density decreases with an increase of water content. - This statement is generally true as well. Beyond the optimum water content, further increases in water content lead to a decrease in dry density due to excessive moisture content.
4. An airless soil will have maximum possible value of dry density for the given water content. - This statement is also generally true. In compaction, removing excess air from the soil allows for achieving the maximum possible dry density for a given water content.