What are univalent elements?

Li, Lithium has one electron in its outer shell. Valence electrons occupy the orbits furthest from the nucleus,

All those listed on the periodic table.

hydrogen is but not oxygen

Yes, the properties of the elements within a period vary from element to element. For example, the metallic character decreases and the non-metallic character increases from left to right within a...

At room temperature, there are 11 gases, and they are hydrogen, nitrogen, oxygen, fluorine, chlorine, and all 6 inert gases, helium, neon, argon, krypton, xenon and radon. It is mercury and bromine...