The correct answer is option 'C' - The Peninsular Plateau.

Explanation:

The Peninsular Plateau is the oldest landmass in India. It is located in the southern part of the country and covers a major portion of the Deccan Plateau.

1. Geological Formation:
The Peninsular Plateau was formed during the Precambrian period, which is the oldest geological period. It is believed to be around 3.4 billion years old. The plateau is made up of hard crystalline rocks like granite, gneiss, and schist, which are characteristic of ancient landmasses.

2. Tectonic Activity:
The Peninsular Plateau has experienced multiple tectonic activities over millions of years. It went through several periods of upliftment, folding, faulting, and volcanic eruptions. These geological processes have shaped the landscape of the plateau, resulting in the formation of hills, valleys, and plateaus.

3. Rivers and Valleys:
The Peninsular Plateau is crisscrossed by several rivers, including the Narmada, Tapti, Godavari, Krishna, and Kaveri. These rivers have carved deep valleys and formed extensive river basins. The valleys are considered to be the oldest in India and bear testimony to the ancient and stable nature of the Peninsular Plateau.

4. Biodiversity:
The Peninsular Plateau is known for its rich biodiversity. It is home to several endemic species of plants and animals. The unique flora and fauna found in the region are a result of its ancient origins and isolation from other landmasses.

5. Mineral Resources:
The Peninsular Plateau is also rich in mineral resources. It contains abundant reserves of minerals like coal, iron ore, manganese, bauxite, and limestone. These minerals have played a significant role in the industrial development of the region.

In conclusion, the Peninsular Plateau is the oldest landmass in India, formed during the Precambrian period. Its ancient geological history, diverse landscapes, rich biodiversity, and abundant mineral resources make it a significant region in the country.