What is the empirical formula for a substance that contains 24.59% phosphorus and 75.41% fluorine by mass?

In order to obtain the empirical formula, first divide each element by its molar mass which can be found in the periodic table. The answer in the first step would be the number of moles of each element. Then divide each element with the lowest number of moles obtained in the first step in this case Phosphorus had the lowest number of moles. Then round it up to the nearest whole number. The empirical formula then is Phosphorus pentafluoride or PF5. 

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.

personal, she chose to do it.