Explain river Indus according to Source, tributaries, area drain and one feature

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Explanation:

Indus River (also called the Sindhū) is one of the longest rivers in Asia. It flows through China (western Tibet), India (Ladakh), and Pakistan.[1] Originating in the Tibetan Plateau in the vicinity of Lake Manasarovar, the river runs a course through the Ladakh region of India,[a] towards Gilgit-Baltistan and then flows in a southerly direction along the entire length of Pakistan to merge into the Arabian Sea near the port city of Karachi in Sindh.[2] It is the longest river in Pakistan.

81 is a composite number.

a mid-ocean ridge or mid-oceanic ridge is an underwater mountain range, formed by plate tectonics. this uplifting of the ocean floor occurs when convection currents rise in the mantle beneath the oceanic crust and create magma where two tectonic plates meet at a divergent boundary.a geomagnetic reversal is a change in a planet's magnetic field such that the positions of magnetic north and magnetic south are interchanged.