Why is Argon(39.94) placed rightly b4 potassium(39.10) in the periodic table?
That is very true but I think the answer they are looking for is that it would be placed before potassium because potassium has an atomic number of 19 (It has 19 protons, 19 neutrons, and 19 electrons in its non-isotopic neutral state) while Argon’s atomic number is 18 (It has 18 protons, 18 neutrons, and 18 electrons in its non-isotopic neutral state). The reason Argon has a larger atomic mass which can be misleading is because the atomic mass is the mean relative atomic mass of an element in the local environment. In other words the atomic mass can differ because its the average of the different isotopes, and potassium must occur naturally with lighter isotopes than Argon does making its average weight lower. But essentially Potassium is after Argon because it has one more proton than Argon does.
