What is the reduction of $Cr_2O_3$ by heating it with aluminum called?

In the MacArthur-Forrest process,which element is used to extract silver from the solution of $Na[Ag(CN)_2]$?

In the manufacture of iron from haematite,the function of limestone is as

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: In the Ellingham diagram,a sharp change in slope of the line is observed for $Mg \rightarrow MgO$ at $\sim 1120^{\circ} C$.
Reason $R$: There is a large change of entropy associated with the change of state.
In the light of the above statements,choose the correct answer from the options given below.

When bauxite powder is mixed with coke and reacted with nitrogen at $2075 \ K$, carbon monoxide and $X$ are formed. What is the gas formed when $X$ is reacted with water?

The materials mixed with the ore before it is subjected to smelting in the extraction of iron are: