The electronic configuration of polonium is $ 2,8,18,32,18,6 $ . It shall gain two electrons. How can it be a metal?

Hint: Metals are the chemical elements that can easily lose electrons and have low values of electronegativities. Metals are also good conductors of heat and electricity. When the electrical conductivity of any chemical element increases with increasing temperature. It means it has a metallic character.

Complete answer:
Polonium is a chemical element with atomic number $ 84 $ in the periodic table. The Nearest inert gas to the polonium element is Radon with atomic number $ 86 $ . By this fact it was clear that polonium is deficient of only two electrons to attain inert gas and tries to gain two electrons which can be non-metallic. The element that can try to attain electrons from another element will be non-metallic.
But polonium exists as a metal which is opposite to the electronic configuration. The given electronic configuration of polonium is $ 2,8,18,32,18,6 $ . It has six electrons in its outer shell and is two electrons deficient to attain stable configuration.
But polonium has a lower value of electronegativity of $ 4 $ . The electrical conductivity of polonium also increases with increase in temperature which is a property of a metal.
Thus, polonium is considered as a metal.

Note:
Electronegativity is defined as the tendency of attraction of the shared pair of electrons towards itself. Non-metals like halogens have higher values of electronegativity whereas metals like alkali and alkaline earth metals have lower electronegativity value. Lower electronegativity value of polonium also leads to it being considered as metal.