An atom with 39 protons and a mass number of 89 what is the number of neutrons

Why are the trends and exceptions to the trends in ionization energy observed?

How many moles of potassium hydroxide are needed to completely react with 2.94 moles of aluminum sulfate according to the following equation:

Henry moseley used x-ray experiments to determine the atomic number of elements. how did his discovery contribute to the development of the periodic table? a.it confirmed that elements should be arranged in strict order of increasing atomic mass. b.it led to elements with similar atomic numbers being grouped together. c.it allowed the elements to be placed in strict order of increasing atomic number. d.it showed that the way mendeleev grouped elements together was completely wrong.