Podzolization is a process of accumulation in soil:

✅ Explanation:
Podzolization is a soil formation process that occurs in cool, humid climates, typically under coniferous or mixed forests. It is characterized by the downward movement (leaching) of iron, aluminum, and organic matter from the upper soil layers, leaving behind a bleached, ash-colored layer rich in silica. This silica-rich layer is known as the eluvial horizon or E horizon.

📌 Other Options Explanations:
-(b) Iron and aluminium oxides: These are leached from the upper horizons (eluviation) and accumulate in the lower horizons (illuviation) during podzolization, forming a reddish-brown layer called the spodic horizon or B horizon.
-(c) CaCO₃ (Calcium carbonate): Calcium carbonate is a base and is readily leached from the soil during podzolization. Its presence is associated with soils in drier climates with less intense weathering.
-(d) CaSO₄ (Calcium sulfate): Similar to calcium carbonate, calcium sulfate is also leached from the soil during podzolization.