$Pb$ and $Sn$ are extracted from their chief ores by:

Explain the extraction of elements by oxidation.

Given below are two statements: One is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: The reduction of a metal oxide is easier if the metal formed is in liquid state than solid state.
Reason $R$: The value of $\Delta G^{\ominus}$ becomes more on negative side as entropy is higher in liquid state than solid state.
In the light of the above statements,choose the most appropriate answer from the options given below.

Extraction of copper by smelting uses silica as an additive to remove

Limestone is present in the blast furnace production of iron in order to
$(I)$ provide a source of $CaO$
$(II)$ remove some impurities
$(III)$ supply $CO_2$

Explain the reduction of metal oxides to metal.