Acertain compound is made up of one phosphorus (p) atom, three fluorine (f) atoms, and one oxygen (o) atom. what is the chemical formula of this compound?

In this item, we are given with the number of atoms of the given elements that would comprise the compound. The chemical formula of a certain compound is usually written with the chemical symbol of the element and then the count (or number) as a subscript. In this regard, the formula for the compound would have to be,

     PF₃O

This compound is known as the PHOSPHORUS FLUORIDE OXIDE. 

True, the standard unit for volume is liters which can be represented by either a lower case "l" or a capital "l"

Nonmetals usually react by gaining electrons