‘Imphal Basin’ surrounded by Manipur hills is a fine example of

The correct answer is A) Lacustrine plain. The Imphal Basin is an intermontane basin enclosed by the Manipur hills, and it was once a large lake. Over time the lake filled with sediment and drained, leaving a flat floor. Such plains formed by deposition in former lakes are called lacustrine plains. The Loktak lake that survives today is a remnant of that older lake system.

• B) Loess plain: Loess is wind-blown silt. Loess plains are found in places like the Huang He basin in China and parts of Europe. Imphal has no such aeolian origin.
• C) Glacial plain: Glacial plains come from glacial deposition or outwash, as in parts of northern Europe and North America. Manipur has no glacial history of this kind.
• D) Alluvial plain: Alluvial plains are built by rivers, like the Indo-Gangetic plain. Rivers do flow through Imphal, but the question's key feature is the enclosing hills and the lake origin, which point to lacustrine.

The concept links to geomorphology of the Northeast and to Mains issues like the Loktak hydroelectric project, flood management and wetland ecology in Manipur.

Trap: Candidates pick alluvial plain because a river flows through the basin. The question asks about the origin of the landform, not the presence of a river.