I'm not quite sure on what i'm supposed to do, i'd appreciate an explanation.

Just find the mass of the oxygen that will be leftover after the chemical reaction of the magnesium and oxygen

each chemical family is represented as a group or column on the periodic table. based on chemical properties, there are 6 types of chemical families. group 1 represents alkali metals, group 2 represents alkaline earth metals, groups 3 to 12 represent transition metals, groups 13 to 16 represent non-metals and other metals, group 17 represents halogens and group 18 represents noble gases.

you gotta add the following molecules so we can give u an answer

explanation: