The element with only one valence electron is hydrogen (H). Hydrogen has one electron in its outermost shell, which gives it a valence of 1.
However, it is important to note that hydrogen is not generally considered a noble element. Noble gases refer to a specific group of elements in the periodic table, including helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). These elements are called noble because they have a full complement of valence electrons in their outermost electron shells, making them stable and unreactive. They exhibit very low reactivity and are resistant to forming chemical bonds with other elements.
The noble gases have completely filled electron shells, except for helium, which has only two electrons in its outermost shell. This full complement of electrons gives them a high degree of stability, and they do not readily gain, lose, or share electrons with other elements. This lack of reactivity is why they are called noble or inert gases.
In contrast, hydrogen, with its single valence electron, is not considered a noble gas. It is highly reactive and can both gain and lose electrons to form various compounds with other elements.