Answer:
As you go down the periodic table, usually atoms get bigger because n gets bigger (there are electrons in higher shells). Effective nuclear charge does get bigger too going down the periodic table, but this effect is smaller than the change in shell.
Explanation:
Au^2S^3+ 3H^2 = 2Au + 3H^2S
Atomic mass deals with the number of protons and neutrons added together, atomic number deals with protons only, though isotopes can be explained like this, say you had a hydrogen atom it's one proton and one electron if you add a neutron to it, the hydrogen becomes Deuterium which is a isotope of hydrogen it's the same atom just a neutron added to it for a different atomic mass if only slightly changed
The answer is homogeneous
