Question

Why argon comes before potassium but has higher mass number than potassium

Answer 1

Atomic number of Argon is 18 and atomic number of Potassium is 19. Whole number atomic mass of Argon is 40 and whole number atomic mass of Potassium is 39.In modern periodic table, the elements are arranged in increasing order of their atomic number not atomic masses. As atomic number of Argon is less than Potassium,it comes before Potassium.