Compared to a potassium atom, a potassium ion has a) a smaller radius b) a larger radius c) fewer protons d) more protons

Potassium is a metal. So when it is ionized, it is to act as a cation, or a positively charged ion, K⁺.  This means that potassium donates an electron when ionized. Thus, it would have lesser electrons and consequently, smaller radius. So, the answer is A.

Hello thereone of the following properties was originally used to arrange elements on the periodic table, but is no longer used to organize the modern version. which property fits this description? answer: atomic mass  was originally used to arrange elements on the periodic table, but is no longer used to organize the modern version.

Order of filling levels and sublevels of electrons: 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s²4d¹⁰5p⁶6s²3f¹⁴5d¹⁰6p⁶for an element with 5 electrons in the 3d energy level: full configuration: 1s²2s²2p⁶3s²3p³.