Small islands formed at the river mouth is called estuary.

Here are the answers to the questions: 1. Small islands formed at the river mouth is called estuary. An estuary is a partially enclosed coastal body of water where freshwater from rivers mixes with saltwater from the ocean. Small islands formed at a river mouth are typically part of a delta*, which is a landform created by the deposition of sediment. The correct option is False*. 2. The development of the undersea rift mountain range is the result of a convergent plate movement. Undersea rift mountain ranges, like the Mid-Ocean Ridge, are formed at divergent plate boundaries, where tectonic plates pull apart, allowing magma to rise and create new crust. Convergent plate movement* involves plates moving towards each other. The correct option is False*. 3. The Himalayas mountain range is the result of a plate subduction between a continental plate and an oceanic plate. The Himalayas were formed by the collision of two continental plates* (the Indian Plate and the Eurasian Plate). While oceanic crust was involved in earlier stages, the mountain range itself is primarily a result of continental-continental collision, not oceanic-continental subduction. The correct option is False*. 4. At the Atlantic Ocean, there is a subduction between the oceanic plates to create the Mid-Atlantic Ridge. The Mid-Atlantic Ridge is a divergent plate boundary where new oceanic crust is formed as plates move apart. Subduction* occurs at convergent plate boundaries where one plate slides beneath another. The correct option is False*. That's 2 down. 3 left today — send the next one.