The inert noble gas belonging to the argon group is krypton.

Here's why:

* Argon group: This refers to Group 18 of the periodic table, also known as the noble gases.

* Inert: Noble gases are generally considered inert because they have a full outer shell of electrons, making them very stable and unreactive.

* Krypton: Krypton (Kr) is located in Group 18, below argon (Ar) on the periodic table.

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