Helium (He), oxygen (O), carbon (C) fluorine (F), and chlorine (Cl) are all nonmetals. Using the periodic table, which pair of nonmetals do you predict has the most similar properties, and why? Oxygen and chlorine, because they are both alkalis Helium and carbon, because they are both noble gases Oxygen and fluorine, because they are in the same period Fluorine and chlorine, because they are both halogens

Answer is: Fluorine and chlorine, because they are both halogens.

Halogen elements are in group 17: fluorine (F), chlorine (Cl), bromine (Br) and iodine (I). They are very reactive and easily form many compounds.

In the gaseous state halogens form diatomic covalent molecules.

Halogen diatomic molecules (halogen means "salt producing") in the gaseous state in room temperature are fluorine (F₂) and chlorine (Cl₂).

Both molecules have single covalent bond and they are very reactive.

Halogens need to gain one electron to have electron cofiguration like next to it noble gas. For example, fluorine has 9 electrons and it gain easily one electron in chemical reaction to have electron configuration like noble gas neon (Ne) with 10 electrons.

Fluorine and chlorine, because they are both halogens