A strontium atom differs from a strontium ion in that the atom has a greater number of electrons
Explanation: Strontium has 2 valence electrons in its outer shell. It is easier to lose these 2...
"Made of" eg of chocolate (=chocolate) of wood (=wooden) of steel (=steel) You do see what the this is made of. "Made from" eg Wine is made from grapes. You don't see the grapes when you look at wine...
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge.