How do electrons fill up a d sublevel

|using the periodic tablewarm-upuse the periodic table in the tools bar to answer the following questions.what elemental classification does oxygen belongto? done

May someone me with these science questions

Which of the following natural processes is most likely to support the formation of an underwater sinkhole? a pollution buildup from deposited minerals b limestone cave collapsing due to changes in sea level c erosion of large amounts of sand moved by ocean waves d oxidation of rock formed by chemical weathering