Question

¹⁹₉A is a metal or non-metal?

Answer 1

The representation ${}_9{}^{19}A$ shows that the atomic number of the said element is 9 and mass number is 19. This shows that the element is Fluorine which is a non-metal. You can also tell the metallic or non-metallic character on the basis of electronic configuration.
Atomic number = 19
Electronic configuration = 2,7
As the valence electrons are more than 4 therefore it is a non-metal. If the valence electrons are less than 4 then it will be a metal.