The periodic table of the elements lists the elements in order of increasing atomic number. Each element has its own unique squa
re in the periodic table. Numbers in an element's square are used to tell how many protons, neutrons and electrons a typical atom of each element has. 
Based on the information shown, which of the following is true about magnesium atoms?
Magnesium has an atomic number of 12 which means it has 12 protons. All Magnesium atoms have 12 protons, the neutrons however may differ which produces things called isotopes where the atoms have same protons but neutrons change.
Keep in mind the atomic number is unique to each element, so 12 atomic number will always be Magnesium, 1 will always be Hydrogen and so on.....