Which is smaller, Se, or O?

Oxygen is much smaller then Selenium, that is because of how high the charge density is.

If you mean electron then O(8 electrons) is smaller than Se(34 electrons).

If you mean atomic mass then O(16) is still smaller than Se(78).

If   Valency then O and Se are the same(-2).

answer; i believe that the correct answer is (a) potassium(k)

cytokinesis is the splitting of a cell membrane to form 2 identical daughter cells. it's similar to mitosis as both cells have identical copies of dna and cytokinesis is a step in the mitotic cycle.