a) The maximum dry density obtained increases with the increase in the compaction effort. The higher the compaction energy applied, the closer will be the packing of the materials leading to high dry density and low Optimum moisture content.

b) Since IS heavy compaction test (modified proctor test) imparts more compaction energy then the IS light compaction test (standard proctor test), so option a) is correct.

c) Fine soils have relatively more OMC but less maximum dry density compared to coarser soil because due to the high specific surface is more water is required for lubrication, hence showing a higher OMC.

d) Fine-grained soils have a higher void ratio, occupying more volume and hence shows a lesser value of maximum dry density compared to coarser soil. Hence option b) is incorrect and d) is correct.

e) Zero air voids line is the line that indicates an imaginary situation where there is no air in the soil and hence the air content in the soil is 0and unit weight corresponding to this condition is called zero air void unit weight and S_r (Degree of saturation) + A_c (Air content) = 1, So the degree of saturation will be 1 for zero air content.

Therefore, option c) is also correct.