ap chemistry question?

Electron configuration....

There is no need to count electrons, Simply look carefully at the electron configuration, and in particular the highest energy sublevel.

[Rn] 7s2, 5f14, 6d10, 7p4

The highest energy sublevel is the 7p, and there are four electrons. What group of elements has 4 p-electrons. Those are the chalcogens (O, S, Se, Te, Po. The period 2 chalcogen is oxygen.

*** By the way, a more "energy-friendly" way to write the electron configuration is by listing the sublevels by increasing energy, rather than using the Aufbau principle, which follows the periodic table.

Use: [Rn] 5f14, 6d10, 7s2, 7p4