Asingle atom of calcium could combine with a single atom of fluorine, creating electron energy stability for both atoms. true false

False. Each atom of calcium needs two atoms of fluorine to create an ionic compound. The atom of calcium could gain stability if it gives the last two electrons in the highest energy level. The fluorine atom only can accept one electron in its highest level of energy to complete it and to reach the lowest energy level. This is the reason because an atom of calcium needs two atoms of fluorine.

If you detect any mistake in my English, please tell me!

Not a  mixture of two common elements that can be separated by physical means.