Oxygen is a non-metal. Cobalt is a metal. Silicon is a metalloid. Chlorine is a non-metal. Hydrogen, nitrogen, oxygen, fluorine, and chlorine are all gasses at room temperature, so they are non-metals. Semiconductors are mostly metalloids. Here are some Quizlet notes to help with the rest. I really recommend using these and maybe bookmark them for future reference! I hope I helped!
https://quizlet.com/26573992/metal-nonmetal-or-metalloid-flash-cards/
https://quizlet.com/2318314/properties-of-metalloids-metals-and-nonmetals-flash-cards/
