Which statement correctly describes whether a compound is a pure substance? a compound is not a pure substance because each of its molecules is made up of the atoms of two or more different elements. a compound is a pure substance because its molecule cannot be broken down into simpler particles by physical means. a compound is not a pure substance because it is not an element, and only elements are pure substances. a compound is a pure substance because it consists of two different elements, which are pure substances.

Answer is: A compound is a pure substance because its molecule cannot be broken down into simpler particles by physical means.

Pure substance is made of only one type of atom (element) or only one type of molecule, it has definite and constant composition with distinct chemical properties. Pure substances can be separated chemically, not physically, that is difference between pure substances and mixtures.

Electrolysis of water (pure substance) is the chemical separation, because from one molecule (water) two molecules (hydrogen and oxygen) are produced. Water is separeted into two molecules:

Reaction of reduction at cathode: 2H⁺(aq) + 2e⁻ → H₂(g).

Reaction of oxidation at anode: 2H₂O(l) → O₂(g) + 4H⁺(aq) + 4e⁻.

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.