Metals, Minerals, Ores: Properties, Uses

21. Cinnabar is an ore of which one of the following ?

Cinnabar is an ore of which one of the following ?

[amp_mcq option1=”Copper” option2=”Zinc” option3=”Mercury” option4=”Manganese” correct=”option3″]

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UPSC NDA-2 – 2021
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Cinnabar is a mineral that is the chief ore of mercury. Its chemical composition is mercury(II) sulfide (HgS). It is known for its distinctive bright red color and is historically important as a source of mercury metal.
Cinnabar is the main ore from which mercury (Hg) is extracted. It is chemically represented as HgS.
Copper ores include chalcopyrite ($\text{CuFeS}_2$) and malachite ($\text{Cu}_2\text{CO}_3(\text{OH})_2$). Zinc ores include sphalerite (ZnS) and calamine (a historical term for zinc ores, including smithsonite ($\text{ZnCO}_3$) and hemimorphite ($\text{Zn}_4\text{Si}_2\text{O}_7(\text{OH})_2 \cdot \text{H}_2\text{O}$)). Manganese ores include pyrolusite ($\text{MnO}_2$).

22. To protect steel and iron from rusting, a thin layer of which one of t

To protect steel and iron from rusting, a thin layer of which one of the following metals is applied ?

[amp_mcq option1=”Magnesium” option2=”Zinc” option3=”Aluminium” option4=”Lead” correct=”option2″]

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Rusting is the process of oxidation of iron, forming hydrated iron(III) oxide. To protect iron and steel from rusting, a protective layer of another metal is applied. Zinc is commonly used for this purpose through a process called galvanization. Zinc is more reactive than iron, and it preferentially corrodes, acting as a sacrificial layer to protect the underlying iron or steel even if the coating is scratched.
Galvanization, the process of coating iron or steel with a thin layer of zinc, is a widely used method to prevent rusting. Zinc acts as a barrier and also provides sacrificial protection (cathodic protection) because it is more electrochemically active than iron.
Other methods to prevent rusting include painting, oiling, greasing, chrome plating, tin plating, and alloying (like making stainless steel). Aluminium is also more reactive than iron and forms a protective oxide layer, but galvanization with zinc is the most common method among the options listed for general anti-rust protection of steel and iron.

23. Which one of the following represents the correct order of electron re

Which one of the following represents the correct order of electron releasing tendency of metals ?

[amp_mcq option1=”Zn > Cu > Ag” option2=”Ag > Cu > Zn” option3=”Cu > Zn > Ag” option4=”Cu > Ag > Zn” correct=”option1″]

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The correct option is A) Zn > Cu > Ag.
The electron releasing tendency of metals is determined by their position in the electrochemical series or reactivity series. Metals higher in the series have a greater tendency to lose electrons and act as reducing agents, thus having higher electron releasing tendency.
The reactivity series orders metals based on their decreasing reactivity: K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au. Zinc is higher in the series than copper, and copper is higher than silver. Therefore, the order of electron releasing tendency is Zn > Cu > Ag. This also corresponds to their relative standard electrode potentials (standard reduction potentials, where less positive or more negative potential indicates higher electron releasing tendency).

24. Zinc is used to protect iron from corrosion because zinc is

Zinc is used to protect iron from corrosion because zinc is

[amp_mcq option1=”more electropositive than iron” option2=”cheaper than iron” option3=”a bluish white metal” option4=”a good conductor of heat and electricity” correct=”option1″]

This question was previously asked in
UPSC NDA-2 – 2017
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Zinc is used to protect iron from corrosion through a process called galvanization. Zinc protects iron because it is more electropositive (or more reactive) than iron. In the electrochemical series, zinc is placed above iron, meaning it loses electrons more easily and has a higher tendency to be oxidized. When both metals are present in the presence of an electrolyte (like moisture), zinc acts as the anode and corrodes sacrificially, while iron acts as the cathode and is protected from oxidation (rusting). Even if the zinc coating is scratched and iron is exposed, the zinc in contact with the electrolyte will still corrode preferentially, providing galvanic protection to the iron.
– Zinc is more electropositive/reactive than iron.
– Zinc acts as a sacrificial anode, corroding instead of iron.
– Provides protection even if the coating is scratched (galvanic protection).
Other methods of protecting iron from rusting include painting, greasing, plating with less reactive metals (like tin, although this doesn’t provide sacrificial protection if scratched), and alloying (like stainless steel). Galvanization is a very effective and widely used method due to zinc’s sacrificial nature.

25. The alkali metals have relatively low melting point. Which one of the

The alkali metals have relatively low melting point. Which one of the following alkali metals is expected to have the highest melting point?

[amp_mcq option1=”Li” option2=”Na” option3=”K” option4=”Rb” correct=”option1″]

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UPSC NDA-2 – 2015
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The alkali metals are in Group 1 of the periodic table: Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Caesium (Cs), and Francium (Fr). Moving down the group, the metallic bonding strength generally decreases due to the increasing atomic size and shielding effect, which weakens the attraction between the positive ions and the delocalized valence electrons. Weaker metallic bonding leads to lower melting points. Therefore, the melting points of alkali metals decrease down the group. Among the options provided (Li, Na, K, Rb), Lithium is at the top of the group and is expected to have the highest melting point.
Melting points of alkali metals decrease down the group (from Li to Fr) due to decreasing metallic bond strength.
The approximate melting points are: Li (180.5 °C), Na (97.8 °C), K (63.5 °C), Rb (39.3 °C), Cs (28.5 °C). As expected, Lithium has the highest melting point among the given options. This trend is a typical example of how physical properties change across a group in the periodic table.

26. The symbol of the element ‘Tungsten’ is:

The symbol of the element ‘Tungsten’ is:

[amp_mcq option1=”Ta” option2=”W” option3=”Tl” option4=”Tc” correct=”option2″]

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The chemical symbol for the element Tungsten is W. The symbol comes from its alternative name, Wolfram, which is derived from the mineral wolframite, a primary source of the element.
The chemical symbol W represents the element Tungsten, derived from the name Wolfram.
Let’s look at the other symbols provided:
A) Ta: Tantalum
C) Tl: Thallium
D) Tc: Technetium
Remembering the symbols for elements is fundamental in chemistry. Tungsten (W) is an important transition metal known for its high melting point.

27. Match List I with List II and select the correct answer using the code

Match List I with List II and select the correct answer using the code given below the Lists:

List I
(Element)		List II
(Use)
A. Li1. Time keeper in atomic clocks
B. Na2. Batteries
C. K3. Transfer of nerve impulses
D. Cs4. Control of the water content in the blood

[amp_mcq option1=”2 3 4 1″ option2=”1 2 3 4″ option3=”2 4 3 1″ option4=”1 3 2 4″ correct=”option3″]

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The correct option is C, 2 4 3 1.
Let’s match the elements with their uses:
A. Li (Lithium): Lithium is a highly reactive alkali metal widely used in batteries, particularly rechargeable lithium-ion batteries that power portable electronic devices, electric vehicles, etc. This matches characteristic 2. (A-2)
B. Na (Sodium): Sodium ions (Na+) are essential electrolytes in the body. They play a critical role in regulating blood pressure and the control of water balance in the blood and body tissues through osmosis. This matches characteristic 4. (B-4)
C. K (Potassium): Potassium ions (K+) are also essential electrolytes involved in various bodily functions, including the transmission of nerve impulses and muscle contractions (along with sodium ions). This matches characteristic 3. (C-3)
D. Cs (Cesium): Cesium is an alkali metal, and the isotope Cesium-133 is famously used in atomic clocks due to the highly stable frequency of radiation emitted during electron transitions in its atom, which defines the length of a second. This matches characteristic 1. (D-1)
Thus, the correct matching is A-2, B-4, C-3, D-1, which corresponds to option C (2 4 3 1).
Elements have a wide range of applications based on their unique chemical and physical properties. Lithium, sodium, and potassium are alkali metals known for their reactivity. Cesium is the heaviest stable alkali metal and is known for its very low ionization energy, making it useful in applications like atomic clocks and photocells.

28. Which one of the following is the correct arrangement of metals in the

Which one of the following is the correct arrangement of metals in the decreasing order of their reactivity ?

[amp_mcq option1=”Iron, Sodium, Silver, Copper” option2=”Silver, Copper, Iron, Sodium” option3=”Sodium, Copper, Silver, Iron” option4=”Sodium, Iron, Copper, Silver” correct=”option4″]

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The reactivity of metals decreases as you move down the reactivity series. The reactivity series ranks metals based on their tendency to lose electrons and undergo oxidation. A metal higher in the series can displace a metal lower in the series from its salt solution. The standard reactivity series places Sodium (Na) very high, followed by Iron (Fe), then Copper (Cu), and finally Silver (Ag) is quite low. Therefore, the decreasing order of reactivity is Sodium, Iron, Copper, Silver.
– Metals are ranked by their reactivity (tendency to lose electrons).
– The reactivity series is K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au > Pt.
– The metals in the options are Sodium (Na), Iron (Fe), Copper (Cu), Silver (Ag).
– Their order in the series is Na > Fe > Cu > Ag.
Highly reactive metals like Sodium react vigorously with cold water. Moderately reactive metals like Iron react with steam. Less reactive metals like Copper and Silver do not react with water or steam and are found uncombined in nature more often.

29. In electrolytic refining of copper, the electrolyte is a solution of

In electrolytic refining of copper, the electrolyte is a solution of

[amp_mcq option1=”acidified copper chloride.” option2=”acidified copper sulphate.” option3=”potassium chloride.” option4=”sodium sulphate.” correct=”option2″]

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In electrolytic refining of copper, the electrolyte is a solution of acidified copper sulphate.
In the process of electrolytic refining, impure copper acts as the anode and dissolves as Cu²⁺ ions, while pure copper acts as the cathode where Cu²⁺ ions from the electrolyte are deposited. The electrolyte needs to contain Cu²⁺ ions, which is achieved by using a solution of copper sulfate (CuSO₄). Sulfuric acid (H₂SO₄) is added to the copper sulfate solution to increase its conductivity and prevent the precipitation of copper hydroxide.
Impurities in the anode that are less reactive than copper (like gold, silver, platinum) settle down as anode mud, while more reactive impurities (like zinc, iron, nickel) dissolve in the electrolyte but do not get deposited on the cathode under controlled voltage.

30. On exposure to moist air, copper gains a green coat on its surface due

On exposure to moist air, copper gains a green coat on its surface due to formation of which one of the following compounds ?

[amp_mcq option1=”Copper carbonate” option2=”Copper oxide” option3=”Copper sulphate” option4=”Copper nitrate” correct=”option1″]

This question was previously asked in
UPSC NDA-1 – 2019
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On exposure to moist air, copper gains a green coat on its surface due to the formation of copper carbonate (more specifically, basic copper carbonate).
When copper is exposed to moist air containing carbon dioxide, it reacts to form a complex mixture of copper carbonates and hydroxides, often referred to as patina. The simplified reaction involves copper reacting with oxygen, water, and carbon dioxide to form basic copper carbonate, typically Cu₂(OH)₂CO₃ (malachite), which has a characteristic green colour.
The reaction is often represented as: 2Cu(s) + H₂O(g) + CO₂(g) + O₂(g) → Cu₂(OH)₂CO₃(s) (basic copper carbonate). While the coating is technically a basic carbonate, “Copper carbonate” (referring to the presence of the carbonate group) is the closest option provided. Pure copper(II) carbonate (CuCO₃) is also green, but the patina is usually a mixture of CuCO₃ and Cu(OH)₂.
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