You can note that the roman numerals in the parenthesis of carbon (IV) oxide and carbon (II) oxide indicate the oxidation state of carbon.
Remember that oxides are compounds that are formed with oxygen and another element, in this case, is carbon. It's important to clarify that the oxidation state of oxygen is always -2. The algebraic sum of the oxidation states must be zero.
One way to distinguish this is to write the oxidation state in every element and then, put these numbers on the other element. Let's see this with the example of carbon (IV) oxide (IV is 4):
And for carbon (II) oxide, we can do the same:
Carbon (IV) oxide is CO2 because the oxidation state of carbon is +4 and carbon (II) oxide is CO because the oxidation state of carbon is +2.
Between the physical properties of CO, we have that it's a colorless compound, at ambient temperature is a gas and it's odorless.
For CO2, it's a gas at an ambient temperature too, it's odorless too at low concentrations and it is denser than air.
