Substances that make up a mixture their own properties once they are combined to form a mixture. . i need to study for finals.

I believe the answer to this is;
Substances that make up a mixture RETAIN their own properties once  they are combined to form a mixture. 
    I believe the answer is RETAIN because the combination in question is a MIXTURE. A mixture is a combination of various substances. In the case of mixtures, all the substances retain their own properties. That is; they remain the way they are and do not change. An example of a mixture is air. And to prove that air is a mixture;
The components of air retain their individual properties.
The components of air cannot be represented by a chemical formula
When the components of air combine, they do not show any form of chemical change, like heat release, change in pressure
  Hope i helped, have a nice day.

It's not the same dearthe first one is in grams per mole while the other is not

Ican't see the chart but the density of both nickel and cobalt is 8.90 g/cm3, so it would be one of those.