Which must be the same when comparing 1 mol of oxygen gas, o2, with 1 mol of carbon monoxide gas, co?

True is ur answer : )

The answer to this is the 3rd choice!

It is a mixture. simply put, a compound must be pure, that is, of only one chemical structure and composition. a mixture is made of different chemical substances (i.e. elements, molecules, compounds) that are not chemically bonded to each other, but instead physically grouped together, as in the case of gasoline (a homogeneous solution).