What is the composition of tungsten?

90% to 97% pure tungsten in a matrix of nickel and copper or nickel and iron.

Explanation:

Heavy metal tungsten alloys are 90% to 97% pure tungsten in a matrix of nickel and copper or nickel and iron. The addition of these alloying elements improves both the ductility and machinability of these alloys over non-alloyed tungsten.

C. The reactant that is used up before the others

Explanation:

The limiting reactant is the reactant that limits the reaction. So when the limiting reactant is used up, the reaction cannot continue.