NEED HELP ASAP ! Which best describes an element?

A. elements are chemicals that are pure substance held together by chemical bonds

B. elements are mixtures of protons, neutrons, and electrons in different combination

C. elements are chemicals that are pure substances represented by symbols that have at least one capital letter

D. elements that are chemicals that are formed when temperature change happens or a precipitate forms

B

Explanation:

I think all options can define element in one form or another but an element is characterized by the atomic number it has i.e you will know it's Carbon due to it's number of protons, neutrons and/or electrons.

alkaline metals are lithium, sodium, rubidium, potassium, cesium and francium.

alkali metals have electronegativity from 0.7 to 1, lowest in periodic table of elements, which means that alkali metals (i group in periodic table) has positive oxidation number in compounds.

electronegativity is a chemical property that describes the tendency of an atom to attract a shared pair of electrons towards itself.

alkaline metals (far left in main group) have lowest ionizations energy and easy remove valence electrons,

for example, potassium is the alkali metal and has a single valence electron in the outer electron shell.

electron configuration of potassium is: ₁₉k 1s²2s²2p⁶3s²3p⁶4s¹.

they can not exist alone in nature, because they are very reactive.