Cobalt-59 is a stable isotope and cobalt-60 is an unstable or radioactive isotope. these two isotopes differ in the number of -

Cobalt-59 and Cobalt-60 differ in that they have different mass number which means they have different number of neutrons. Isotopes are atoms of the same element with similar atomic number but different mass number. Cobalt-60, has a number of uses, which includes, being used to irradiate food sources as a method of preserving food, used in industrial radiography to detect structural flaws in metal parts among other uses. 

Yes it would be a physical change.

All the elements are arranged by melting points on the periodic table. in row they go from metals to gasses. in the row from sodium to argon, sodium is more reactive than the one on its right, magnesium.