Which among the following is a nonferrous alloy?

Given below are two statements:
Statement $I$: During electrolytic refining,the pure metal is made to act as anode and its impure metallic form is used as cathode.
Statement $II$: During the Hall-Heroult electrolysis process,purified $Al_2O_3$ is mixed with $Na_3AlF_6$ to lower the melting point of the mixture.
In the light of the above statements,choose the most appropriate answer from the options given below:

Percentage of silver in German silver is (in $\%$)

Steel contains

In the leaching of $Ag_2S$ with $NaCN$,a stream of air is also passed. It is because of

Select the incorrect statement.