Some people in Manipur live in house built on floating islands of weeds and decaying vegetation held together by suspended silt. These are called:

Answer: (c) Phoomdis

Phumdis are floating mats of vegetation and soil on Loktak Lake (Manipur); Keibul Lamjao park floats on them.

The idea

A floating island need not be solid rock. Interwoven vegetation, organic matter and soil can form a buoyant mat on a lake. Such a mat provides a surface for plants and animals even though water lies below it.

Aquatic plants grow → Dead vegetation accumulates → Roots bind organic matter and soil → A floating mat forms → Living plants grow on it → A floating wetland habitat develops

Why the others are wrong

(a) Tipis are tents of North American tribes.

(b) Barkhans are crescent sand dunes.

(d) Izba is a Russian log hut.

Also know

Keibul Lamjao National Park lies on Loktak’s phumdis and shelters the sangai, the brow-antlered deer. A barchan is a crescent-shaped sand dune. Loktak is a freshwater lake, unlike the brackish coastal lagoons Chilika and Pulicat.