Carbon cannot be used to produce magnesium by chemical reduction of $MgO$ because

During the extraction of silver,which of the following is formed?

In a blast furnace,iron oxide is reduced by which of the following?

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A:$ In an Ellingham diagram,the oxidation of carbon to carbon monoxide shows a negative slope with respect to temperature.
Reason $R:$ $CO$ tends to get decomposed at higher temperature.
In the light of the above statements,choose the correct answer from the options given below:

Given below are two statements.
Statement $I:$ The choice of reducing agents for metals extraction can be made by using Ellingham diagram,a plot of $\Delta G$ vs temperature.
Statement $II:$ The value of $\Delta S$ increases from left to right in Ellingham diagram.
In the light of the above statements,choose the most appropriate answer from the options given below:

After froth flotation,copper sulfide is reduced by.........