What is the full name of this element?

199X

1 Answer
Sep 19, 2016

This is atomic fluorine.

Explanation:

The 9 subscript is the atomic number for 199X, and such an atomic number, Z, specfies the element fluorine. Most fluorine nuclei contain 10 neutrons, and thus the 19F isotope predominates.

As the element, fluorine largely exists as the F2 molecule, which is the most reactive element on the Periodic Table.