Answer: A. 1:1
Explanation: Magnesium has two valence electrons while sulphur has six valence electrons. In the reaction between magnesium and sulphur, one atom of magnesium gives its two valence electrons to one atom of sulphur, resulting in a positively charged magnesium ion (cation) and a negatively charged sulphide ion (anion). This is because all elements in their respective groups want to attain a stable octet structure with the exception of the group eight elements (noble gases). This stable octet structure can be achieved by either a loss, gain or share of electrons.