Why has the arrangement of the periodic table changed over time? A. Mendeleev had not placed the elements in any particular order.

B. The atomic number of an element changes so the table is frequently rearranged.

C. The table was rearranged to show elements in order of increasing atomic number rather than increasing atomic weight.

D. Elements are removed from the table once they can no longer be found in nature.

the formula would be mgso4

mgso[subscript]4

nacl or sodium chloride is an ionic compound. this is because an ionic compound pertains to a compound that consists of positively and negatively charged ions. in this case, na (sodium) has a tendency to lose one electron when it reacts with with other atoms, so the resulting sodium ion contains 11 protons and 10 electrons, thus making it positively charged (na+), when chlorine reacts, it usually gains one electron to form an ion called chloride, thus making it negatively charged ( since the ions are oppositely charged, they attract.