Here's why:

* Atomic Number: Ununtrium has an atomic number of 113, meaning it has 113 protons and 113 electrons.

* Electron Configuration: The electron configuration of ununtrium is [Rn] 5f¹⁴ 6d¹⁰ 7s² 7p¹.

* Valence Electrons: Valence electrons are the electrons in the outermost shell of an atom, and they participate in chemical bonding. In this case, the outermost shell is the 7th shell, and it contains 3 electrons (7s² 7p¹).

Therefore, ununtrium has 3 valence electrons.