Question

Which of the following metals can not be extracted by the carbon reduction process?
(A) Pb
(B) Al
(C) Sn
(D) Zn

Answer 1

To solve this question we first need to know what the carbon reduction process is. The process that uses a carbon reaction to extract metals from their ore oxides and carbon act as a reducing agent is known as the carbon reduction process.

Complete answer:
Upon the calcination and roasting of the ore, an oxide is obtained. This oxide is further reduced by either hydrogen or by carbon.
When ores are heated in the presence of a reducing agent, metals (mostly transition metals) can be extracted. This process is known as thermal reduction.
Now, for the reduction process, the coke form or the carbon monoxide (CO) form of carbon is used.
Carbon cannot reduce all metals. The ability of carbon to reduce a metal is based upon its relative reactivity as compared to the metal. Carbon can only reduce those metal oxides whose metals have less reactivity than carbon.
Now, the relative reactivity of metals and elements can be determined from the reactivity series.
Now, the reactivities of elements are as follows:
$K > Na > Ca > Mg > Al > C > Zn > Fe > Ni > Sn > Pb > H > Cu > Hg > Ag > Au > Pt$
Here, the most reactive metal, potassium (K) is placed at the top of the series whereas the least reactive metal, platinum (Pt) is placed at the bottom of the series.
We can see that among the given elements, zinc (Zn), tin (Sn), and lead (Pb) are less reactive than carbon (C) whereas aluminum (Al) is more reactive than carbon.

Therefore option (B) Al metal cannot be extracted by the carbon reduction process.

Note:
It should be noted that during the extraction process, and reducing an oxide ore to metal, if carbon is used it is oxidized to carbon monoxide, and if carbon monoxide is used, it is oxidized to carbon dioxide. The carbon is present in a positive oxidation state.