Question

I have 2 questions:

Answer 1

The reactivity depends on the elements valence electrons. The need to be stable will make an element become more reactive, In order for an atom to be stable, it needs 8 valence electrons in its outer shell. 

Since Calcium is in group 2, it has 2 valence electrons, and would rather give up the electrons. While Sulfur has 6, it would need to gain 2 more to be stable, making it more reactive. 

Answer 2

An atoms valence is the amount of electrons in the outer ring and atoms like to have a valence of 8 so the closer to having 8 in the outer ring the more reactive the atom is so since both elements are 2 away from a valence of 8 theyre equally reactive