Inorganic Chemistry

21. Which one of the following statements is not correct ?

Which one of the following statements is not correct ?

”Bleaching
” option2=”Bleaching powder acts as a reducing agent in many chemical industries” option3=”Bleaching powder is also known as chlorinated lime” option4=”Bleaching powder is used for disinfecting drinking water” correct=”option2″]
This question was previously asked in
UPSC CAPF – 2016
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Statement B is incorrect. Bleaching powder (Calcium oxychloride, CaOCl₂) is a strong oxidizing agent due to the presence of available chlorine. It acts as an oxidizing agent in bleaching processes and disinfection, not a reducing agent. Reducing agents donate electrons or hydrogen atoms, while oxidizing agents accept electrons or remove hydrogen atoms. Bleaching powder facilitates oxidation reactions.
Understanding the chemical properties of common substances like bleaching powder, specifically its role as an oxidizing agent, is important.
Statement A is correct: Bleaching powder is prepared by passing chlorine gas over dry slaked lime [Ca(OH)₂]. The reaction is Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O.
Statement C is correct: Bleaching powder is also known as chlorinated lime or calcium hypochlorite.
Statement D is correct: Bleaching powder is widely used for disinfecting drinking water, swimming pools, and sanitation purposes because its oxidizing action kills bacteria and other microorganisms.

22. Which one of the following statements is correct ?

Which one of the following statements is correct ?

Iron sulphate and copper sulphate crystals have same number of water of crystallization
Iron sulphate and zinc sulphate crystals have same number of water of crystallization
Zinc sulphate and copper sulphate crystals have same number of water of crystallization
Iron sulphate, copper sulphate and zinc sulphate crystals each have same number of water of crystallization
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UPSC CAPF – 2015
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The statement that is correct is that Iron sulphate and zinc sulphate crystals have the same number of water of crystallization.
Crystals of hydrated salts contain a definite number of water molecules incorporated within their crystal structure. This water is called water of crystallization.
– Iron(II) sulphate (Ferrous sulphate) commonly crystallizes as the heptahydrate, FeSO4.7H2O.
– Copper(II) sulphate commonly crystallizes as the pentahydrate, CuSO4.5H2O.
– Zinc sulphate commonly crystallizes as the heptahydrate, ZnSO4.7H2O.

Comparing the number of water molecules:
– Iron sulphate (7) and Copper sulphate (5): Different number.
– Iron sulphate (7) and Zinc sulphate (7): Same number.
– Zinc sulphate (7) and Copper sulphate (5): Different number.
– Iron sulphate (7), Copper sulphate (5), and Zinc sulphate (7): Not all have the same number.

The number of water molecules in a hydrated crystal is specific to the compound and the conditions under which it crystallized. Common hydrated salts often encountered in chemistry include copper(II) sulphate pentahydrate (blue vitriol), iron(II) sulphate heptahydrate (green vitriol), and zinc sulphate heptahydrate (white vitriol).

23. 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
(Application)
A. Isotope of Uranium 1. Treatment of cancer
B. Isotope of Cobalt 2. Treatment of goitre
C. Isotope of Iodine 3. Treatment of secondary cancer
D. Isotope of Radium 4. Nuclear fuel

Code :

A B C D
(a) 3 2 1 4
(b) 4 2 1 3
(c) 4 1 2 3
(d) 3 1 2 4
A-3, B-2, C-1, D-4
A-4, B-2, C-1, D-3
A-4, B-1, C-2, D-3
A-3, B-1, C-2, D-4
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UPSC CAPF – 2015
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The correct matching is A-4, B-1, C-2, D-3.
– Isotopes of Uranium, specifically Uranium-235, are widely used as fuel in nuclear power plants because they are fissile.
– Cobalt-60 is a radioactive isotope of cobalt used in radiotherapy for the treatment of cancer.
– Iodine-131 is a radioactive isotope of iodine used in the treatment of goitre and thyroid cancer due to its accumulation in the thyroid gland.
– Radium isotopes, particularly Radium-226, were historically used in brachytherapy (a type of radiotherapy) for treating various cancers, including secondary cancers (metastases), although its use has largely been replaced by other isotopes like Cobalt-60 or Iridium-192 due to safety concerns and availability.
Radioisotopes have numerous applications in medicine, industry, and research, utilizing their radioactive properties or as tracers. Their specific application depends on the element’s chemical properties, the isotope’s half-life, and the type and energy of radiation emitted.

24. 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 (Compound)
A. Urea
B. Hydrous copper sulphate
C. Lead sulphide
D. Potassium permanganate
List-II (Colour)
1. Blue
2. White
3. Pinkish purple
4. Black
Code :

A B C D
(a) 2 1 4 3
(b) 2 4 1 3
(c) 3 4 1 2
(d) 3 1 4 2
(a)
(b)
(c)
(d)
This question was previously asked in
UPSC CAPF – 2015
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Matching the compounds with their typical colours: A. Urea is a white crystalline solid (2). B. Hydrous copper sulphate (CuSO₄·5H₂O) is commonly known as blue vitriol and has a distinctive blue colour (1). C. Lead sulphide (PbS) is a black solid (4). D. Potassium permanganate (KMnO₄) is a dark purple solid that forms intense pinkish-purple solutions (3). The correct match is A-2, B-1, C-4, D-3.
Many chemical compounds have characteristic colours, which can be used for identification or in analytical chemistry. The colour arises from the absorption and reflection of light due to the electronic structure of the compound, particularly in transition metal compounds like copper sulphate and potassium permanganate, or in some ionic or covalent compounds.
Anhydrous copper sulphate (CuSO₄) is white; the blue colour appears upon hydration. Potassium permanganate is a strong oxidizing agent and its colour changes upon reduction, which is used in titrations.

25. Arsenic present in groundwater can be partially removed

Arsenic present in groundwater can be partially removed

along with removal of iron by precipitation/coagulation method if iron is also present in the water
on boiling even if iron is absent in the water
on UV-treatment
on filtration even if iron is absent in the water
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UPSC CAPF – 2013
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The correct option is A. Arsenic present in groundwater can be partially removed along with removal of iron by precipitation/coagulation method if iron is also present in the water.
One effective method for removing arsenic from water is co-precipitation or adsorption onto iron oxyhydroxides. When iron is present in the water, or is added as a coagulant (like ferric chloride), iron precipitates are formed. Arsenic species (arsenite and arsenate) adsorb onto the surface of these precipitates or are incorporated into the growing iron particles. Subsequent sedimentation and filtration of these iron precipitates effectively remove arsenic from the water.
Other methods for arsenic removal include adsorption onto activated alumina, iron oxides, or activated carbon, ion exchange, and membrane filtration (reverse osmosis). Boiling (B), UV treatment (C), or simple filtration without precipitation (D) are not effective methods for removing dissolved arsenic from water.

26. Villagers in some parts of India use the water extract of the ash obta

Villagers in some parts of India use the water extract of the ash obtained by burning banana plant as a substitute of soda. Which one of the following is the major active component in the extract ?

Sodium Carbonate
Potassium Carbonate
Calcium Oxide
Magnesium Oxide
This question was previously asked in
UPSC CAPF – 2009
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The major active component in the water extract of ash obtained by burning banana plants, used as a substitute for soda, is Potassium Carbonate.
Plants absorb minerals from the soil, including potassium, sodium, calcium, and magnesium. When plant material is burned, the organic components are removed, leaving behind the mineral residues, primarily as carbonates or oxides. Banana plants are known to accumulate significant amounts of potassium. Burning plant material rich in potassium leads to the formation of potassium carbonate (K₂CO₃). This alkali compound, when extracted with water, yields a solution of potassium carbonate, which has alkaline properties similar to soda (sodium carbonate or sodium bicarbonate).
Historically, wood ash was a common source of potassium carbonate (potash), used in making soap, glass, and as a leavening agent (pearl ash). Different plant species yield ash with varying compositions, but potassium is often a dominant cation in land plants.

27. Which of the following anions has a valency of –3 ?

Which of the following anions has a valency of –3 ?

Nitride
Nitrate
Sulphide
Sulphate
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The correct answer is A) Nitride.
Valency, in the context of ions, refers to the magnitude of the charge on the ion. An anion is a negatively charged ion.
– Nitride is the anion formed from a nitrogen atom gaining electrons to achieve a stable electron configuration. Nitrogen is in Group 15 and typically gains 3 electrons to form N³⁻. Thus, the valency of the nitride ion is -3.
– Nitrate is the polyatomic anion NO₃⁻, with an overall charge of -1.
– Sulphide is the anion formed from a sulphur atom gaining electrons. Sulphur is in Group 16 and typically gains 2 electrons to form S²⁻. The valency of the sulphide ion is -2.
– Sulphate is the polyatomic anion SO₄²⁻, with an overall charge of -2.
The charge on the ion directly corresponds to its valency (with the sign indicating whether it’s a cation or anion). Therefore, the anion with a valency of -3 is Nitride (N³⁻).

28. Consider the following reaction : Fe 2 O 3 (s) + 2Al(s) → 2Fe(s) + Al

Consider the following reaction :
Fe2O3(s) + 2Al(s) → 2Fe(s) + Al2O3(s)
Which of the following statements about the given reaction is NOT correct ?

It is an example of displacement reaction
It is highly endothermic reaction
Fe<sub>2</sub>O<sub>3</sub> acts as oxidizing agent
This reaction is applicable to joining of railway tracks
This question was previously asked in
UPSC NDA-2 – 2023
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The statement that is NOT correct about the given reaction is that it is highly endothermic reaction.
The reaction Fe2O3(s) + 2Al(s) → 2Fe(s) + Al2O3(s) is known as the thermite reaction. It is a highly exothermic reaction, releasing a large amount of heat. Aluminum is more reactive than iron and displaces iron from its oxide, making it a displacement reaction. Fe2O3 is reduced (loses oxygen), so it acts as an oxidizing agent. The large amount of heat produced makes this reaction useful for welding, including joining railway tracks.
The thermite reaction releases so much heat that the iron produced is in a molten state, which is essential for its application in welding. An endothermic reaction absorbs heat from the surroundings, which is the opposite of what happens in the thermite process.

29. Which one of the following is the chemical formula of Plaster of Paris

Which one of the following is the chemical formula of Plaster of Paris ?

$ ext{CaSO}_4 cdot rac{1}{2} ext{ H}_2 ext{O}$
$ ext{CaSO}_4 cdot 2 ext{ H}_2 ext{O}$
$ ext{CaSO}_4 cdot 5 ext{ H}_2 ext{O}$
$ ext{CaSO}_4 cdot 4 ext{ H}_2 ext{O}$
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UPSC NDA-2 – 2021
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The correct option is A. The chemical formula of Plaster of Paris is Calcium Sulfate hemihydrate, which is $\text{CaSO}_4 \cdot \frac{1}{2} \text{ H}_2\text{O}$.
Plaster of Paris is produced by heating Gypsum ($\text{CaSO}_4 \cdot 2 \text{ H}_2\text{O}$) to about 150°C (302°F). This heating process removes three-quarters of the water of crystallization, leaving the hemihydrate form. When mixed with water, Plaster of Paris rehydrates and sets into a hard mass, which is chemically Gypsum.
Gypsum ($\text{CaSO}_4 \cdot 2 \text{ H}_2\text{O}$) is Calcium Sulfate dihydrate. It is a naturally occurring mineral. The setting of Plaster of Paris is an exothermic reaction: $\text{CaSO}_4 \cdot \frac{1}{2} \text{ H}_2\text{O} + 1\frac{1}{2} \text{ H}_2\text{O} \rightarrow \text{CaSO}_4 \cdot 2 \text{ H}_2\text{O}$.

30. Which one of the following pairs of elements is liquid at room tempera

Which one of the following pairs of elements is liquid at room temperature and at normal pressure ?

Gallium and Bromine
Mercury and Bromine
Gallium and Mercury
Gallium and Caesium
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UPSC NDA-2 – 2021
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At standard room temperature (approximately 25°C) and normal pressure, only two elements are liquids: Mercury (Hg), a metal, and Bromine (Br₂), a non-metal.
– Mercury is the only metallic element that is liquid at room temperature.
– Bromine is the only non-metallic element that is liquid at room temperature.
– Gallium (melting point 29.8 °C) and Caesium (melting point 28.5 °C) melt just above typical room temperature but are usually considered solid at 25°C.
While Gallium and Caesium have very low melting points and can melt in slightly warmer conditions or even in the hand, Mercury and Bromine are consistently liquid under standard room temperature conditions.
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