Chemistry

171. Consider the following reaction : 2HgO ⎯⎯→ 2Hg + O₂ The respective sta

Consider the following reaction :
2HgO ⎯⎯→ 2Hg + O₂
The respective state of HgO, Hg and O₂ in the above reaction is

[amp_mcq option1=”Liquid, solid, gas” option2=”Solid, solid, gas” option3=”Liquid, solid, liquid” option4=”Solid, liquid, gas” correct=”option4″]

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Mercuric oxide (HgO) is a solid compound at room temperature. Mercury (Hg) is the only metal that exists as a liquid at room temperature. Oxygen (O₂) is a gas at room temperature. Therefore, the respective states of HgO, Hg, and O₂ are solid, liquid, and gas.
The physical states of substances at standard temperature and pressure (or implied conditions) are important in chemical reactions. Mercury is unique among metals in being liquid at room temperature.
This reaction represents the thermal decomposition of mercuric oxide. Heating HgO breaks it down into its constituent elements, mercury and oxygen. The states indicated correspond to the stable forms of these substances under normal conditions after the reaction.

172. Which one of the following metals does NOT react with cold water to li

Which one of the following metals does NOT react with cold water to liberate hydrogen gas ?

[amp_mcq option1=”Potassium” option2=”Iron” option3=”Calcium” option4=”Sodium” correct=”option2″]

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Iron (Fe) is a less reactive metal compared to Potassium (K), Sodium (Na), and Calcium (Ca). Highly reactive metals like K and Na react vigorously with cold water, producing hydrogen gas and metal hydroxides. Calcium also reacts with cold water, though less vigorously, producing hydrogen gas and calcium hydroxide. Iron, however, does not react with cold water. It reacts slowly with hot water and vigorously with steam to produce hydrogen gas and metal oxide.
The reactivity of metals determines their reaction with water. More reactive metals displace hydrogen from cold water; moderately reactive metals displace hydrogen from hot water or steam; less reactive metals do not react with water at all.
The general order of reactivity of these metals with water is K > Na > Ca > Fe. Potassium and Sodium react violently with cold water. Calcium reacts steadily with cold water. Iron reacts with steam (very hot water) to form iron oxides and hydrogen gas.

173. Which one of the following processes involves chemical reaction ?

Which one of the following processes involves chemical reaction ?

[amp_mcq option1=”Evaporation of petrol” option2=”Dissolution of salt in water” option3=”Storing of oxygen gas under pressure in a gas cylinder” option4=”Burning of magnesium ribbon in air” correct=”option4″]

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Burning of magnesium ribbon in air involves a chemical reaction.
A chemical reaction involves the rearrangement of atoms and molecules to form new substances with different chemical properties. Evaporation, dissolution, and storing gas under pressure are physical processes where the substance’s chemical composition remains unchanged, only its state or distribution changes. Burning (combustion) is a chemical process where a substance reacts rapidly with oxygen, typically producing heat and light and forming new chemical compounds. When magnesium burns in air, it reacts with oxygen and nitrogen to form magnesium oxide and magnesium nitride, respectively.
Evaporation is a phase transition from liquid to gas. Dissolution is the process of dissolving a solute in a solvent to form a solution; the solute particles disperse but do not chemically change. Storing gas under pressure is a physical change affecting density and volume. Burning involves chemical transformation.

174. 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
(Chemical process)		List II
(Reaction)
A. Electrolysis of water1. Double displacement reaction
B. Burning of coal2. Combination reaction
C. Iron nail immersed in copper sulphate solution3. Decomposition reaction
D. Addition of barium chloride solution to aluminium sulphate solution4. Displacement reaction

Code :

ABCD
(a)3421
(b)4213
(c)3241
(d)4123

[amp_mcq option1=”(a) 3 4 2 1″ option2=”(b) 4 2 1 3″ option3=”(c) 3 2 4 1″ option4=”(d) 4 1 2 3″ correct=”option3″]

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The correct matching of chemical processes with their reaction types is A-3, B-2, C-4, D-1.
A. Electrolysis of water involves breaking down water (a single compound) into hydrogen and oxygen (simpler substances) using electricity. This is a decomposition reaction. (H₂O → H₂ + O₂)
B. Burning of coal involves the reaction of carbon (and other components) with oxygen, usually forming carbon dioxide. This is a combination reaction (C + O₂ → CO₂) and also combustion.
C. Iron nail immersed in copper sulphate solution involves iron displacing copper from copper sulphate because iron is more reactive than copper. This is a displacement reaction. (Fe + CuSO₄ → FeSO₄ + Cu)
D. Addition of barium chloride solution to aluminium sulphate solution involves the exchange of ions between the two reactants, forming new compounds, one of which is insoluble (barium sulphate precipitate). This is a double displacement reaction. (3BaCl₂ + Al₂(SO₄)₃ → 3BaSO₄↓ + 2AlCl₃)
Matching these gives: A-3, B-2, C-4, D-1, which corresponds to option (c).

175. 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 ?

[amp_mcq option1=”It is an example of displacement reaction” option2=”It is highly endothermic reaction” option3=”Fe2O3 acts as oxidizing agent” option4=”This reaction is applicable to joining of railway tracks” correct=”option2″]

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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.

176. Buckminster fullerene, which looks like a football, is an allotropic f

Buckminster fullerene, which looks like a football, is an allotropic form of

[amp_mcq option1=”Phosphorus” option2=”Sulfur” option3=”Carbon” option4=”Tin” correct=”option3″]

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Buckminster fullerene, which looks like a football, is an allotropic form of Carbon.
Allotropes are different structural modifications of an element. Carbon exists in several allotropic forms, including diamond, graphite, graphene, and fullerenes. Buckminster fullerene, also known as C60, is the most well-known fullerene molecule, consisting of 60 carbon atoms arranged in a spherical structure resembling a soccer ball (truncated icosahedron).
Fullerenes were discovered in 1985 by Robert Curl, Harold Kroto, and Richard Smalley, who were awarded the Nobel Prize in Chemistry in 1996 for their work. Other allotropes of carbon like diamond and graphite are well-known for their distinct physical properties arising from different atomic arrangements. Phosphorus, Sulfur, and Tin also have allotropes, but fullerenes are specific to Carbon.

177. Which one of the following alloys contains a non-metal as one of its c

Which one of the following alloys contains a non-metal as one of its constituent ?

[amp_mcq option1=”Brass” option2=”Bronze” option3=”Amalgam” option4=”Steel” correct=”option4″]

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Steel is an alloy that contains a non-metal, Carbon, as one of its primary constituents.
An alloy is a mixture of metals or a mixture of a metal and another element. Brass is an alloy of copper and zinc (both metals). Bronze is typically an alloy of copper and tin (both metals). An amalgam is an alloy of mercury with another metal (both mercury and the other element are metals). Steel is primarily an alloy of iron and carbon, where carbon is a non-metal. The carbon content in steel ranges from about 0.2% to 2.1% by weight.
The presence of carbon significantly alters the properties of iron, increasing its strength and fracture resistance compared to pure iron. The amount of carbon affects the steel’s properties; for instance, higher carbon content generally leads to harder and stronger steel but also makes it more brittle.

178. Galvanization is a method of protecting iron from rusting by coating w

Galvanization is a method of protecting iron from rusting by coating with a thin layer of

[amp_mcq option1=”Gallium” option2=”Aluminum” option3=”Zinc” option4=”Silver” correct=”option3″]

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Galvanization is a method of protecting iron from rusting by coating it with a thin layer of Zinc.
Galvanization works by providing a barrier coating of zinc to prevent corrosive substances from reaching the underlying iron or steel. More importantly, zinc acts as a sacrificial anode. This means that zinc is more reactive than iron and will corrode preferentially, even if the coating is scratched and the iron is exposed.
Rusting is the corrosion of iron, which occurs when iron reacts with oxygen and water. Zinc protects iron through both barrier protection and sacrificial protection. Other metals like aluminum or silver are not typically used for galvanization of iron; aluminum is sometimes used in different protective coatings (like anodizing for aluminum itself), and silver is too expensive and not suitable for this application.

179. C 4 H 8 belongs to the homologous series of

C4H8 belongs to the homologous series of

[amp_mcq option1=”alkanes” option2=”alkenes” option3=”alkynes” option4=”cycloalkanes” correct=”option2″]

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The correct answer is alkenes.
Homologous series are a series of compounds with the same general formula, usually differing by a single methylene (CH₂) unit. The general formula for alkanes is CnH2n+2, for alkenes is CnH2n (with one double bond), and for alkynes is CnH2n-2 (with one triple bond). For n=4, C₄H₈ fits the general formula CnH2n, which corresponds to alkenes. While cycloalkanes also have the formula CnH2n, alkenes are the primary open-chain homologous series with this formula.
C₄H₈ can represent various isomers, including but-1-ene, but-2-ene, 2-methylpropene (isobutylene), and cyclobutane or methylcyclopropane. Among the given options for homologous series, alkenes are the direct fit for the formula CnH2n in the context of typical classification alongside alkanes and alkynes.

180. The number of structural isomers of pentane is

The number of structural isomers of pentane is

[amp_mcq option1=”5″ option2=”4″ option3=”2″ option4=”3″ correct=”option4″]

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The correct answer is 3.
Structural isomers are compounds with the same molecular formula but different arrangements of atoms. Pentane has the molecular formula C₅H₁₂. The three structural isomers of pentane are:
1. n-pentane (a straight chain of five carbon atoms).
2. Isopentane (2-methylbutane, a four-carbon chain with a methyl group attached to the second carbon).
3. Neopentane (2,2-dimethylpropane, a three-carbon chain with two methyl groups attached to the central carbon).
As the number of carbon atoms increases in alkanes, the number of possible structural isomers grows rapidly. For example, hexane (C₆H₁₄) has 5 isomers, and heptane (C₇H₁₆) has 9 isomers.
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