Chemistry

121. Which one of the following compounds is NOT considered an acid ?

Which one of the following compounds is NOT considered an acid ?

[amp_mcq option1=”BF₃” option2=”AlCl₃” option3=”NH₃” option4=”C₆H₅OH” correct=”option3″]

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UPSC CAPF – 2015
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A) BF₃ (Boron Trifluoride) is a Lewis acid because the Boron atom has an incomplete octet and can accept an electron pair.
B) AlCl₃ (Aluminum Chloride) is also a Lewis acid as the Aluminum atom has an incomplete octet and can accept an electron pair.
C) NH₃ (Ammonia) is a Brønsted-Lowry base because it can accept a proton (H⁺) to form ammonium ion (NH₄⁺). It is also a Lewis base because the nitrogen atom has a lone pair of electrons that it can donate. It is not considered an acid in standard definitions.
D) C₆H₅OH (Phenol) is a weak acid because the hydroxyl group (-OH) attached to the benzene ring can donate a proton, forming the phenoxide ion. The acidity is enhanced by the stability of the phenoxide ion through resonance.
Therefore, NH₃ is the compound that is NOT considered an acid; it is a base.
Acids can be defined in various ways (Arrhenius, Brønsted-Lowry, Lewis). Brønsted-Lowry acids are proton donors. Lewis acids are electron pair acceptors. Bases are proton acceptors (Brønsted-Lowry) or electron pair donors (Lewis). Ammonia is a common example of a base.
Lewis acidity is particularly relevant for species like BF₃ and AlCl₃, which lack a hydrogen ion to donate but can accept electron pairs. Phenol is a classic example of an organic acid, albeit a weaker one compared to carboxylic acids, with a pKa of around 10.

122. The hydrogen atoms present in acetylene molecule are :

The hydrogen atoms present in acetylene molecule are :

[amp_mcq option1=”acidic” option2=”basic” option3=”both acidic and basic” option4=”neutral” correct=”option1″]

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UPSC CAPF – 2015
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Acetylene has the chemical formula C₂H₂ and a linear structure H-C≡C-H. The carbon atoms in acetylene are sp hybridized. sp hybridized orbitals have higher s-character (50%) compared to sp² (33.3%) or sp³ (25%) hybridized orbitals. Higher s-character means the electrons in the C-H bond are held more closely to the carbon nucleus due to the greater penetration of the s orbital. This makes the carbon atom more electronegative than sp² or sp³ hybridized carbons, and consequently, it pulls electron density away from the hydrogen atom. This makes the C-H bond weaker and the hydrogen slightly positive, allowing it to be removed as a proton (H⁺) by a strong base. Therefore, the hydrogen atoms in acetylene are acidic.
The acidity of terminal alkynes (like acetylene) is due to the high electronegativity of the sp-hybridized carbon atom to which the hydrogen is attached. This polarizes the C-H bond, making the proton relatively easy to remove.
Acetylene is a weak acid, much weaker than carboxylic acids or mineral acids, but significantly more acidic than alkanes or alkenes. It can react with very strong bases, such as sodium amide (NaNH₂), to form acetylide salts (e.g., Na⁺ [C≡CH]⁻ or Na⁺ [C≡C]⁻ Na⁺). This acidic property is utilized in certain organic synthesis reactions.

123. Which one of the following statements is correct ?

Which one of the following statements is correct ?

[amp_mcq option1=”Iron sulphate and copper sulphate crystals have same number of water of crystallization” option2=”Iron sulphate and zinc sulphate crystals have same number of water of crystallization” option3=”Zinc sulphate and copper sulphate crystals have same number of water of crystallization” option4=”Iron sulphate, copper sulphate and zinc sulphate crystals each have same number of water of crystallization” correct=”option2″]

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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).

124. 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 Uranium1. Treatment of cancer
B. Isotope of Cobalt2. Treatment of goitre
C. Isotope of Iodine3. Treatment of secondary cancer
D. Isotope of Radium4. Nuclear fuel

Code :

ABCD
(a)3214
(b)4213
(c)4123
(d)3124

[amp_mcq option1=”A-3, B-2, C-1, D-4″ option2=”A-4, B-2, C-1, D-3″ option3=”A-4, B-1, C-2, D-3″ option4=”A-3, B-1, C-2, D-4″ correct=”option3″]

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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.

125. 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 :

ABCD
(a)2143
(b)2413
(c)3412
(d)3142

[amp_mcq option1=”(a)” option2=”(b)” option3=”(c)” option4=”(d)” correct=”option1″]

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.

126. Which one of the following statements regarding baking powder is NOT c

Which one of the following statements regarding baking powder is NOT correct ?

[amp_mcq option1=”It is a mixture” option2=”It forms bubbles in a wet mixture” option3=”It can be used instead of using yeast” option4=”It does not contain sodium bicarbonate” correct=”option4″]

This question was previously asked in
UPSC CAPF – 2015
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Baking powder is a chemical leavening agent that is a mixture of a base (typically sodium bicarbonate, NaHCO₃, also known as baking soda), a weak acid (such as cream of tartar, sodium aluminium sulfate, or monocalcium phosphate), and sometimes a starch filler. Statement D claims that baking powder does not contain sodium bicarbonate, which is false.
Sodium bicarbonate is a fundamental component of baking powder. When moistened, the acid and sodium bicarbonate react to produce carbon dioxide gas, which creates bubbles (leavening) in doughs and batters.
Options A, B, and C are correct statements about baking powder. A) It is a mixture of different chemical compounds. B) The reaction upon wetting produces carbon dioxide bubbles. C) It is used as an alternative leavening agent to yeast, providing a quicker rise without fermentation.

127. The following item consists of two statements, Statement I and Stateme

The following item consists of two statements, Statement I and Statement II. Examine these two statements carefully and select the correct answer using the code given below :
Code :
Statement I : Catalytic hydrogenation is highest when the catalyst remains in the powdered form
Statement II : When a catalyst is in the powdered form, its surface area becomes highest

[amp_mcq option1=”Both the statements are individually true and Statement II is the correct explanation of Statement I” option2=”Both the statements are individually true but Statement II is NOT the correct explanation of Statement I” option3=”Statement I is true but Statement II is false” option4=”Statement I is false but Statement II is true” correct=”option1″]

This question was previously asked in
UPSC CAPF – 2015
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Statement I says that catalytic hydrogenation is highest when the catalyst is in powdered form. Statement II says that when a catalyst is in powdered form, its surface area becomes highest. Both statements are individually true, and Statement II correctly explains why Statement I is true.
Catalysis occurs on the surface of the catalyst. A larger surface area provides more active sites for the reaction to take place, thus increasing the reaction rate. Powdering a solid increases its total surface area significantly.
Heterogeneous catalysis involves the catalyst being in a different phase from the reactants, often a solid catalyst with gaseous or liquid reactants. In such systems, the surface area of the solid catalyst is a crucial factor affecting the reaction kinetics. Increasing the surface area (e.g., by powdering or using porous materials) generally increases the rate of heterogeneous catalytic reactions.

128. Which of the following are not chemical changes ? 1. Tempering of iron

Which of the following are not chemical changes ?
1. Tempering of iron
2. Conversion of iron piece into an electro-magnet by passing the current around the iron
3. Melting of iron
4. Rusting of iron
Select the correct answer using the code given below :

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

This question was previously asked in
UPSC CAPF – 2014
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A chemical change involves the formation of new substances with different chemical properties. A physical change alters the form or appearance of a substance but not its chemical composition.
1. Tempering of iron: This is a heat treatment process that changes the microstructure and properties (like hardness and toughness) of iron alloys (steel). While it involves heat, it primarily changes the physical state and crystalline structure, not the fundamental chemical composition of the iron or steel. It is considered a physical process.
2. Conversion of iron piece into an electro-magnet by passing the current: When electric current passes around an iron core, it becomes a temporary magnet. This is a physical phenomenon (magnetism) induced by the electric current. The iron itself does not undergo a chemical transformation.
3. Melting of iron: This is a change of state from solid to liquid. The chemical composition of iron remains Fe. This is a physical change.
4. Rusting of iron: Iron reacts with oxygen and water to form hydrated iron(III) oxides (rust, typically Fe2O3.nH2O). This is a chemical reaction that produces new substances with different chemical properties than iron. This is a chemical change.
The question asks which are *not* chemical changes. These are the physical changes: 1 (Tempering), 2 (Electromagnetism), and 3 (Melting).
Identify the difference between chemical changes (formation of new substances) and physical changes (change in form, state, or appearance without changing chemical composition).
Examples of chemical changes include burning, rusting, digestion, and cooking. Examples of physical changes include melting, freezing, boiling, cutting, and bending. Magnetism is a physical property. Heat treatments like tempering involve physical changes in material properties.

129. Which one among the following is not a form of carbon?

Which one among the following is not a form of carbon?

[amp_mcq option1=”Graphene” option2=”Graphite” option3=”Fullerene” option4=”Quartz” correct=”option4″]

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UPSC CAPF – 2013
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D) Quartz
Allotropes are different structural modifications of an element in the same physical state.
– Graphene, Graphite, and Fullerene are all allotropes of carbon. Graphene is a single layer of carbon atoms in a hexagonal lattice. Graphite is composed of multiple layers of graphene stacked together. Fullerenes are carbon molecules forming hollow spheres, ellipsoids, or tubes (like buckyballs).
– Quartz, on the other hand, is a mineral composed of silicon and oxygen, with the chemical formula SiO2 (silicon dioxide). It is a major component of the Earth’s crust. Therefore, quartz is not a form of carbon.
Other common allotropes of carbon include diamond and amorphous carbon. The different physical properties of these allotropes (e.g., hardness, conductivity) are due to the different ways the carbon atoms are bonded together.

130. Arsenic present in groundwater can be partially removed

Arsenic present in groundwater can be partially removed

[amp_mcq option1=”along with removal of iron by precipitation/coagulation method if iron is also present in the water” option2=”on boiling even if iron is absent in the water” option3=”on UV-treatment” option4=”on filtration even if iron is absent in the water” correct=”option1″]

This question was previously asked in
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.
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