Landforms

Diastrophism is the correct term for the processes that form and change major features of Earth's crust, including folding, faulting, and mountain building. Geomorphism refers to landform study, isomerism is a chemistry concept, and catastrophism is an outdated geological theory.

Nile is the longest river (length = 6653 km).

An ox-bow lake forms when a meandering river creates a U-shaped bend that gets cut off from the main channel. Over time, erosion and deposition narrow the neck of the meander until the river breaks through, abandoning the bend and creating a standalone U-shaped water body. It's a fluvial process, not related to glaciers or sea waves.

The Mid-Atlantic Ridge is a classic example of a diverent plate boundary where tectonic plates are moving apart. As the plates separate, magma rises to create new oceanic crust, causing seafloor spreading. Convergent boundaries involve plates coming together, transform boundaries involve plates sliding past each other, and 'spreading boundary' is not a standard geological term.

The Ganges-Brahmaputra Delta (also known as the Sundarbans Delta) is the world's largest river delta, formed by the confluence of the Ganges and Brahmaputra rivers. It covers approximately 105,000 square kilometers and spans across Bangladesh and India. The Seine-Rhine forms a smaller European delta, the Danube flows into the Black Sea, and while the Nile forms a large delta, it is formed by a single river, not a pair.

A tarn is a mountain lake or pool formed in a cirque excavated by a glacier. These are typically found in corries (cirques) carved by glacial erosion and are often deep and clear. In contrast, oxbow lakes are formed by river meanders, yardangs are wind-eroded rock formations, and ridges are linear elevated landforms not specifically created by glaciers.

Abyssal plains are extensive, flat regions of the ocean floor that lie between the continental margins (where the ocean depth increases rapidly) and the mid-ocean ridges (where new oceanic crust is formed). They are among the flattest and smoothest regions on Earth, covered by fine-grained sediments. The other options are not standard geomorphological terms for ocean floor features.

Correct answer is (3). 

Parabolic dunes are formed when vegetation partially covers the sand surface, anchoring the dune arms while the center remains mobile. This creates a U-shaped dune with the horns pointing upwind (opposite to barchans). Barchans are crescent-shaped dunes without vegetation, seifs are longitudinal dunes, and levees are river deposits, not dune types.

 Faulting helps in the formation of rift valley.

A caldera is a large collapsed depression formed when a volcano erupts and empties its magma chamber, causing the ground above to collapse downward. This creates a crater much larger than typical volcanic vents. Calderas are not lava types, small mouths, or necessarily multi-vented volcanoes - they are specifically the collapsed basins left after massive eruptions.

Playas are shallow, flat-floored desert depressions formed by the deflating action of winds, which remove fine sediments and leave behind a flat, often salt-encrusted surface. They are characteristic of arid regions where wind erosion is dominant. They are not formed by glacial, river, or marine erosion processes.