NEET General Principles and Processes of Isolation of Elements Previous Year Questions with Solutions

The blast furnace is divided into thermal zones based on height: (a) Upper lower-temperature zone (500 K to 800 K), and (b) Middle-to-lower higher-temperature zone (900 K to 1500 K):

At the top of the furnace, haematite (Fe₂O₃) is reduced in stages by carbon monoxide at 500 K – 800 K:

In the 900 K to 1500 K zone, carbon dioxide is reduced by coke, FeO is reduced to iron, and limestone forms slag:

Reaction (2), Fe₂O₃ + CO ⟶ 2 FeO + CO₂, takes place strictly at the lower temperatures (500 K – 800 K). Therefore, it does NOT occur in the 900 K to 1500 K range:

Mercury ($Hg$, atomic number 80) is the only metallic element that exists in the liquid state at standard room temperature ($25^\circ\text{C}$ / $298\text{ K}$), having a melting point of $-38.83^\circ\text{C}$.

NCERT categorizes metal refining processes based on physical properties: - Distillation: Used specifically for metals with low boiling points, such as Zinc ($Zn$) and Mercury ($Hg$). The impure volatile metal is vaporized and condensed as pure distillate, leaving non-volatile impurities behind. - Electrolysis: Applied to reactive or common industrial metals like copper, aluminum, and gold. - Zone Refining: Applied to ultra-pure semiconductors (Germanium, Silicon, Boron, Gallium, Indium). - Chromatography: Utilized when elements to be separated are available in minute quantities and exhibit close chemical similarities.

Distillation is the designated metallurgical method to obtain highly pure mercury, corresponding to Option (3).

In the industrial metallurgy of iron (extraction from haematite $Fe_2O_3$), the blast furnace exhibits a continuous vertical temperature gradient: - Top Zone (Reduction Zone): $500\text{ K} - 800\text{ K}$ - Middle Zone (Slag Formation & Reduction of FeO): $900\text{ K} - 1500\text{ K}$ - Lower Zone (Combustion & Fusion Zone): $1500\text{ K} - 2200\text{ K}$

At the bottom of the blast furnace, oxygen in the blast of hot air burns descending coke to generate carbon dioxide and immense thermal energy:

According to NCERT Metallurgy, the intense heat released in this localized exothermic reaction drives the temperature up to about 2200 K in the combustion zone.

The iron obtained from blast furnace is pig iron, which contains about 4% carbon and many impurities (S, P, Si, Mn). Wrought iron (malleable iron) is the purest form of commercial iron, containing less than 0.2-0.5% carbon, prepared by oxidising impurities in a reverberatory furnace lined with haematite. Thus, Statement (1) is completely false.

During copper smelting in the Bessemer converter, the auto-reduction reaction occurs: $$2\text{Cu}_2\text{O} + \text{Cu}_2\text{S} \to 6\text{Cu} + \text{SO}_2\uparrow$$ As the molten copper solidifies, dissolved $$\text{SO}_2$$ escapes, creating blisters on the surface (blister copper). Statement (2) falsely claims the blisters are due to $$\text{CO}_2$$.

Nickel is refined by the Mond Process, where it is heated with carbon monoxide to form volatile nickel tetracarbonyl ($$\text{Ni(CO)}_4$$). The Van Arkel method is used for refining zirconium ($$\text{Zr}$$) and titanium ($$\text{Ti}$$) via their volatile iodides. Thus, Statement (3) is false.

Pig iron obtained from the blast furnace is tapped into moulds (historically named "pigs" and "sows") and can be melted and moulded into diverse commercial shapes and castings (or converted into cast iron and steel). Hence, Statement (4) is the designated correct statement in NTA official key.