2 elements with same properties as K could be rubidium and sodium. Elements in the same column (vertical) will have similar properties to each other
Mg has 12 protons- this is given on the (generally) the top left of the element on the periodic table. We know protons have a positive charge so to make the element neutral there would be 12 electrons to balance the protons. The neutrons is usually the same number as the protons but since the majority of an atoms weight is in protons and neutrons- electrons mass in negligee it’s so small- you can subtract the number of protons from the mass number. In this case : 24-12= 12. So there are 12 neutrons
