The correct answer is option 'D', Northern plains.

Explanation:
The formation of physiographic features is influenced by various factors such as tectonic activity, erosion, weathering, and deposition. Alluvial deposits, which are sedimentary materials transported and deposited by rivers, play a significant role in the formation of certain landforms. One such physiographic region formed due to alluvial deposits is the Northern plains in India.

Northern Plains:
The Northern plains in India are a vast low-lying region that stretches from the foothills of the Himalayas to the Arabian Sea. It is a fertile and densely populated region, known as the "breadbasket" of India. The formation of the Northern plains is primarily attributed to the deposition of alluvial sediments by major rivers like the Indus, Ganges, and Brahmaputra.

Formation:
1. Rivers: The Himalayan rivers, originating from the lofty mountains, carry a massive amount of sediment load due to the erosion caused by the steep slopes and fast-flowing water. These rivers deposit the sediments in the relatively flat and stable regions downstream, leading to the formation of the Northern plains.
2. Sediment Deposition: As the rivers enter the plain areas, they slow down their velocity due to the decreased slope. This decrease in velocity causes the sediment load to settle and get deposited on the riverbed and floodplains.
3. Floodplains and Deltas: The rivers meander across the plains, forming wide floodplains. During the monsoon season, when the rivers are in spate, they overflow their banks, depositing sediments across the floodplain. Over time, this repeated deposition leads to the formation of fertile agricultural land.
The rivers also form deltas at their mouths, where the sediments are deposited in the form of fan-shaped landforms. The Ganges-Brahmaputra delta is the largest delta in the world and is a prominent feature of the Northern plains.

Characteristics:
1. Fertile Soil: The alluvial deposits in the Northern plains consist of fine particles such as silt, clay, and sand. These deposits make the soil highly fertile, suitable for agriculture.
2. Flat Topography: The Northern plains have a relatively flat and gently sloping topography, which makes it an ideal region for agricultural activities.
3. River Systems: The region is crisscrossed by several major rivers, which not only provide water for irrigation but also serve as important transportation routes.

Conclusion:
In conclusion, the Northern plains in India are formed due to the deposition of alluvial sediments brought by major rivers like the Ganges, Brahmaputra, and Indus. These sediments have created a vast and fertile plain region that supports extensive agriculture and human habitation.