Which fact is most basic for understanding India's size?

Correct answer: India's area

The governing concept is that the size of a country is measured primarily by the extent of its territory. Area expresses how much surface the country occupies and is therefore the most direct numerical basis for understanding its size. India’s area is commonly stated as about 3.28 million square kilometres. The national sport, national song, and currency may be cultural or administrative facts, but none measures territorial extent. Thus option A is correct because it directly represents the physical space occupied by India. A useful distinction is that area is two-dimensional, whereas distance or length describes only one-dimensional extent.