Fr

because its really low in the rective series and is hard to tarnish.

None at all, silver is less rective than copper

NO, sure not.

Helium (He) mass = 4 g/mol

Fluorine gas (F2) mass = 2*19 = 38 g/mol (almost 10 times heavier),

although fluorine gas hardly can be held stable: it is so VERY rective, even in air!!

I think you mean are the properties of salt different from the elements that it is made up from.

Sodium chloride is common salt that we put on our food.

It has formula of NaCl amd is made up of the elemnts sodium and chlorine. Sodium is a highly rective metal that rects violently with water. Chlorine is poisonous gas at room temperature. So yes. This is a feature of compunds they often have very different properties from their constituent elements.