Concept:An organic soil is one with a high content of decomposed plant and animal matter.
Explanation:Histosols are characterised by a deep surface layer of pure organic material.
They form under wet conditions like peat bogs, where decomposition is slow.
This results in a soil rich in organic matter from dead plants and animals.
In contrast, Aridisols are desert soils with very low organic matter.
Oxisols develop in hot, humid equatorial climates and are rich in iron and aluminium oxides, not organic matter.
Vertisols are high in clay (over 30%) and become hard when dry, but are not predominantly organic.
Therefore, among the given options, only Histosols qualify as organic soil.
Answer:Histosols.