In the context of the physical geography of India, which of the following major geographical divisions is considered the oldest in terms of geological formation and stability?

Introduction / Context:
Indian geography divides the country into several broad physical divisions such as the Northern mountains, the Northern plains, the Peninsular plateau, and the coastal plains. Questions about which of these is geologically the oldest test understanding of plate tectonics and the geological history of the Indian landmass. The Peninsular region, often called the Peninsular plateau, is known for its ancient, stable rocks and is considered the oldest part of the Indian landmass.

Given Data / Assumptions:
- The question refers to major geographical divisions of India.- Options include the Northern mountainous region, Ganga-Brahmaputra Plain, Peninsular region, and Coastal plain.- We need to identify which division is geologically the oldest and most stable.

Concept / Approach:
The Peninsular plateau consists mainly of ancient igneous and metamorphic rocks. It is a part of the Gondwana landmass and has remained relatively stable for hundreds of millions of years. In contrast, the Himalayas and the Northern plains are geologically younger, formed due to the collision of the Indian plate with the Eurasian plate and subsequent sediment deposition. Coastal plains are also younger accumulations along the margins of the plateau and plains.

Step-by-Step Solution:
Step 1: Recall that the Northern mountainous region, including the Himalayas, is among the youngest mountain ranges in the world, formed in the Cenozoic era.Step 2: The Ganga-Brahmaputra Plain is an alluvial plain formed by deposition of sediments brought down by the Himalayan rivers, which makes it relatively young.Step 3: Coastal plains along the eastern and western coasts of India are thin strips of alluvial and marine deposits and are not the oldest formations.Step 4: The Peninsular region is composed of very old rocks, part of the stable shield known as the Indian Shield, dating back to the Precambrian period.Step 5: Therefore, the Peninsular region is correctly identified as the oldest geographical division among the options.

Verification / Alternative Check:
Standard school and exam oriented geography textbooks clearly state that the Peninsular plateau is the oldest and most stable landmass in India. It includes plateaus like the Deccan, Malwa, and Chotanagpur, which have experienced long periods of erosion rather than active mountain building. This matches the reasoning above and confirms the answer.

Why Other Options Are Wrong:
Northern mountainous region: The Himalayas are geologically young fold mountains and are still rising, so they cannot be the oldest division.Ganga-Brahmaputra Plain: This is an alluvial plain composed of relatively recent river deposits lying at the foothills of the Himalayas.Coastal plain: These plains are narrow and formed by marine and fluvial deposits along the edges of older landmasses, so they are younger than the Peninsular plateau.

Common Pitfalls:
Some learners confuse altitude with geological age and assume that high mountains must be older. In reality, old mountains are often worn down to plateaus, while young mountains like the Himalayas are high and sharply folded. Remembering that the Peninsular plateau is a very old, stable block of crust helps avoid such confusion in multiple choice questions.

Final Answer:
Peninsular region is the oldest major geographical division of India in terms of geological formation.