Within the main group (A) elements, atomic size generally * A. remains constant within a period
C. increases as you move down a group
D. cannot be predicted

The correct answer is c

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

Answerthe same as;

D. h2o + h2o > h3o + oh- confirmed.