5. If you combine 15.6 g Mg with 13.9 g of Br, what is the percent composition of each element in the mixture.

since the atomic number is the number of protons in the nucleus, as we move to the left on the periodic table, the electrostatic pull between the nucleus and the valence electron shell decreases. as we move down a group (vertical column), the valence shell energy level gets further and further from the nucleus.

its first and third is your answer i did the qustion the fourth isnt right