Final answer:
The child of Loki known as the Midgard serpent that encircles the whole world is Jormungandr. Jormungandr is a key figure in Norse mythology, signifying the end of the world when it releases its tail.
Step-by-step explanation:
The child of Loki known as the Midgard serpent that encircles the whole world is Jormungandr. This massive serpent is a central figure in Norse mythology and is one of Loki's three children.
According to the myth, Jormungandr grew so large that it could encircle the Earth and grasp its own tail. When it releases its tail, Ragnarok, the end of the world, would begin.
This serpent is not to be confused with figures from other mythologies, such as the depiction of a serpent wrapped around a lion on the larger runestone of Harald Bluetooth or the serpent-form taken by Zeus in Orphism.
Jormungandr is unique to Norse myth and is also known for its epic battle with the god Thor.