Need

1s² 2s² 2p⁶ 3s² 3p⁵ is the electron configuration for which element? *

fluorine
chlorine
sulfur
bromine

Chlorine.

If you search Google images for "Aufbau principle periodic table," you'll find some handy diagrams that will make it much easier to determine an element based on its electron configuration. Determine the number of electrons in the last part of the configuration (in this case, 5), locate that group on the Aufbau periodic table diagram, then count that number from left to right within that group. In this case, within the "3p" portion of the Periodic table, count to 5 and you'll find Chlorine as the answer.