What material was left by the Indus River floods to enhance agricultural productivity?

The correct answer is silt, as it plays a crucial role in enhancing agricultural productivity in regions affected by river floods. Silt is a fine sediment that is typically deposited by river systems during flooding events. When the Indus River floods, it overflows its banks and spreads this nutrient-rich silt over the surrounding floodplain.

This silt contains essential minerals and organic matter that are vital for plant growth, replenishing the soil and making it more fertile. The combination of moisture and nutrients allows for better crop yields, contributing significantly to the agricultural practices in the Indus Valley. This natural process of sediment deposition strengthens the soil structure and enhances its ability to retain water, further supporting agricultural productivity in the area.