To answer this question, you need to be familiar with the names of chemical elements.
Option A) Arsenic - This option is incorrect because Arsenic is not named after Copenhagen, Denmark.
Option B) Cobalt - This option is incorrect because Cobalt is not named after Copenhagen, Denmark.
Option C) Hafnium - This option is correct. Hafnium is named after Copenhagen, Denmark. The name "Hafnium" is derived from "Hafnia," which is the Latin name for Copenhagen.
Option D) Copper - This option is incorrect because Copper is not named after Copenhagen, Denmark.
The correct answer is C) Hafnium. This option is correct because Hafnium is the element that is named after Copenhagen, Denmark.