The correct answer is option 1: Radon is an inert gas.

Inert gases, also known as noble gases, are a group of elements that have full outer electron shells, making them chemically stable and unreactive. Radon, with the chemical symbol Rn, is a member of this group. It is a colorless, odorless, and tasteless gas.

Option 2, stating that radon is an artificial fiber, is incorrect. Radon is a naturally occurring element and is not associated with artificial fibers.

Option 3, stating that radon is explosive, is also incorrect. While radon is a radioactive gas, it is not inherently explosive. It does not react with other elements to produce an explosion.

Option 4, stating that radon is a metal, is incorrect as well. Radon is a noble gas and does not possess the characteristics of a metal.

Therefore, the only correct option is option 1, which accurately describes radon as an inert gas.