Chemistry

131. Diamond is a polymorph of graphite. Both contain carbon atoms, but the

Diamond is a polymorph of graphite. Both contain carbon atoms, but they have extremely different properties because of the condition in which they are formed. Diamond is obtained after applying

[amp_mcq option1=”very high pressure and low temperature” option2=”very low pressure and high temperature” option3=”very low pressure and low temperature” option4=”very high pressure and high temperature” correct=”option4″]

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The correct option is D. Diamond is formed under conditions of very high pressure and high temperature deep within the Earth’s mantle.
Diamond and graphite are both allotropes (polymorphs) of carbon. Their dramatically different properties (hardness, electrical conductivity, etc.) arise from their different crystal structures, which are formed under vastly different pressure and temperature conditions. Graphite is the stable form of carbon at standard conditions, while diamond is stable only at extremely high pressures and temperatures.
Natural diamonds are formed at depths of 140 to 190 kilometers (87 to 118 miles) in the Earth’s mantle, where pressures are between 45 and 60 kilobars and temperatures are between 900 and 1,300 degrees Celsius (1,650 to 2,370 degrees Fahrenheit). Synthetic diamonds are also created using high-pressure high-temperature (HPHT) or chemical vapor deposition (CVD) methods, simulating similar extreme conditions.

132. Natural gas is a mixture of gases and contains mainly

Natural gas is a mixture of gases and contains mainly

[amp_mcq option1=”methane and higher hydro-carbons” option2=”butane and isobutene” option3=”methane only” option4=”methane, hydrogen and carbon monoxide” correct=”option1″]

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Natural gas is a naturally occurring hydrocarbon gas mixture. The primary component of natural gas is methane (CH₄), which is the simplest hydrocarbon molecule. However, natural gas is typically not pure methane. It also contains varying amounts of other, heavier gaseous hydrocarbons such as ethane (C₂H₆), propane (C₃H₈), butane (C₄H₁₀), and pentane (C₅H₁₂), commonly referred to as higher hydrocarbons or natural gas liquids (NGLs). In addition to hydrocarbons, natural gas can contain non-hydrocarbon gases such as carbon dioxide (CO₂), nitrogen (N₂), hydrogen sulfide (H₂S), and trace amounts of other gases like helium. The question asks for the main components. While methane is the most abundant component, “methane and higher hydro-carbons” accurately describes the primary composition.
Natural gas is a mixture, predominantly methane, but also containing other light hydrocarbons.
The exact composition of natural gas varies depending on the source (gas field). Raw natural gas must be processed to remove impurities and heavier hydrocarbons before it can be distributed and used as fuel. The higher hydrocarbons are often separated and sold as valuable byproducts (NGLs).

133. In most of the children’s toys, a toxic chemical remains present. In t

In most of the children’s toys, a toxic chemical remains present. In this respect, which among the following statements is/are correct?

  • 1. The name of the toxic element is phthalates which are esters of phthalic acid.
  • 2. They are mainly used as plasticizers, i.e., substances added to plastics to increase their flexibility and longevity.
  • 3. They are easily released into environment because there is no covalent bond between the phthalates and plastics in which they are mixed.

Select the correct answer using the code given below.

[amp_mcq option1=”1 only” option2=”2 only” option3=”Both 1 and 2″ option4=”Neither 1 nor 2″ correct=”option3″]

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Based on the provided options which only evaluate statements 1 and 2, the correct option is C, stating that both 1 and 2 are correct.
The question refers to a toxic chemical commonly found in children’s toys, known as phthalates. Phthalates are used to make plastics more flexible and durable.
Statement 1: The toxic elements often found in plastics, especially in toys, are phthalates, which are esters of phthalic acid. This statement is correct.
Statement 2: Phthalates are primarily used as plasticizers, substances added to plastics to increase their flexibility, transparency, durability, and longevity. This statement is correct.
Statement 3: Phthalates are not covalently bonded to the plastic polymer matrix; they are mixed into the plastic. This allows them to leach out or be released into the environment (including into a child’s mouth if the toy is chewed). This statement is also correct.
However, the provided options A, B, C, D only offer combinations involving statements 1 and 2. Evaluating only statements 1 and 2 against these options: Statement 1 is correct, and Statement 2 is correct. Therefore, “Both 1 and 2” is the correct option among the choices given.

134. Which one among the following salts causes hardness to the water?

Which one among the following salts causes hardness to the water?

[amp_mcq option1=”Calcium bicarbonate” option2=”Calcium carbonate” option3=”Sodium sulphate” option4=”Potassium chloride” correct=”option1″]

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Water hardness is caused by dissolved multivalent cations, primarily calcium (Ca²⁺) and magnesium (Mg²⁺) ions. These ions are usually present in water as salts like bicarbonates, sulfates, or chlorides.
Calcium bicarbonate (Ca(HCO3)₂) is a common salt found dissolved in water that causes temporary hardness. When heated, calcium bicarbonate decomposes to form calcium carbonate, which precipitates out, reducing the hardness. Calcium carbonate (CaCO₃) itself is largely insoluble in water under normal conditions and does not dissolve significantly to cause hardness.
Sodium salts (like sodium sulphate) and potassium salts (like potassium chloride) do not cause water hardness, as sodium (Na⁺) and potassium (K⁺) are monovalent ions. The term “hardness” specifically refers to the presence of divalent or trivalent metallic cations.

135. Bleaching powder is added in water used for drinking purpose. The role

Bleaching powder is added in water used for drinking purpose. The role of bleaching powder in this case is

[amp_mcq option1=”of disinfectant” option2=”of bleaching agent” option3=”to remove impurity” option4=”to decrease the pH” correct=”option1″]

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Bleaching powder (Calcium hypochlorite, Ca(ClO)2) is commonly added to water for drinking purposes because it releases chlorine, which acts as a powerful disinfectant. Chlorine kills or inactivates harmful microorganisms such as bacteria, viruses, and protozoa that can cause waterborne diseases.
The disinfecting action of bleaching powder is due to the hypochlorite ion (ClO⁻) and hypochlorous acid (HClO) formed when it dissolves in water. HClO is a strong oxidizing agent.
While bleaching powder is a bleaching agent in other contexts (due to its oxidizing properties), its primary role in water treatment for drinking is disinfection. It does not directly remove dissolved impurities or significantly decrease the pH of the water at typical treatment concentrations.

136. When an iron nail is dipped in a solution of copper sulphate, the iron

When an iron nail is dipped in a solution of copper sulphate, the iron nail becomes brownish in colour and the blue colour of copper sulphate solution fades after some time. The reaction is an example of chemical

[amp_mcq option1=”combination” option2=”decomposition” option3=”displacement” option4=”double displacement” correct=”option3″]

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When an iron nail is dipped in a solution of copper sulphate (CuSO4), a chemical reaction occurs. Iron (Fe) is more reactive than copper (Cu), so it displaces copper from the copper sulphate solution. The reaction is: Fe (s) + CuSO4 (aq) → FeSO4 (aq) + Cu (s). This results in a brownish deposit of copper on the iron nail and the blue colour of the copper sulphate solution fading as iron sulphate (FeSO4), which is light green, is formed.
This type of reaction, where a more reactive element displaces a less reactive element from its compound, is called a displacement reaction.
Combination reactions involve two or more substances combining to form a single product. Decomposition reactions involve a single compound breaking down into two or more simpler substances. Double displacement reactions involve the exchange of ions between two compounds.

137. 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 IList II
A. Iron oxide1. Glossy finish on wood and steel
B. Varnish2. Colourless shining protective coating on wood
C. Enamel paint3. Exterior and interior brick walls
D. Emulsion paint4. Preparatory coating on steel

Code :

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

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The correct matching is A-4, B-2, C-1, D-3. Iron oxide is often used as a preparatory coating or primer on steel to prevent rust. Varnish is a clear, colourless coating that provides a protective and shining finish, typically on wood. Enamel paint dries to a hard, durable, often glossy finish and is used on surfaces like wood and metal. Emulsion paint is a water-based paint commonly used on interior and exterior walls, including brick walls.
– Iron oxide primers (like red oxide) are widely used for corrosion protection on steel.
– Varnish provides a clear, protective layer, enhancing the natural look of wood.
– Enamel paints are known for their hard, glossy finish and durability on various surfaces.
– Emulsion paints are standard for architectural use on walls.
Different types of paints and coatings are formulated for specific purposes, surfaces, and desired finishes. Primers (like iron oxide based) prepare the surface for the topcoat and improve adhesion and durability. Varnishes are transparent finishes. Enamels provide opaque, durable finishes. Emulsions are typically water-based and dry relatively quickly, making them popular for internal walls.

138. Which one among the following statements is correct ?

Which one among the following statements is correct ?

[amp_mcq option1=”Melting of ice and burning of candle represent the same kind of chemical change” option2=”Melting of ice is a physical change and burning of candle is a chemical change” option3=”Melting of ice is a chemical change and burning of candle is a physical change” option4=”Melting of ice and burning of candle represent the same kind of physical change” correct=”option2″]

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UPSC CAPF – 2011
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The correct option is B. Melting of ice is a physical change because water changes its state from solid (ice) to liquid (water), but its chemical composition (H₂O) remains the same. Burning of a candle is a chemical change because the wax (a complex hydrocarbon) reacts with oxygen in the air to produce new substances like carbon dioxide, water vapor, soot, heat, and light.
The question differentiates between physical changes (alteration in form, not composition) and chemical changes (formation of new substances).
Other examples of physical changes include boiling, freezing, condensation, sublimation, breaking glass, and dissolving salt in water (where the salt can be recovered). Examples of chemical changes include rusting of iron, cooking food, digestion, photosynthesis, and explosion of fireworks.

139. Heavy water is so called because it

Heavy water is so called because it

[amp_mcq option1=”contains a number of salts as in sea water” option2=”is the mercury contaminated water” option3=”is saline water used in hospitals” option4=”contains the heavier isotope of hydrogen in water” correct=”option4″]

This question was previously asked in
UPSC CAPF – 2011
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The correct option is D. Heavy water, chemically represented as D₂O, contains deuterium, which is an isotope of hydrogen. Unlike the common hydrogen atom (protium, ¹H) which has only a proton, deuterium (²H or D) has a proton and a neutron, making it approximately twice as heavy as protium. Therefore, water molecules formed with deuterium (heavy water) are heavier than those formed with protium (ordinary water, H₂O).
The question asks for the reason why heavy water is called “heavy”. It relates to its chemical composition and the presence of a heavier isotope of hydrogen.
Heavy water is primarily used as a neutron moderator in certain types of nuclear reactors (pressurized heavy water reactors – PHWRs) because deuterium has a lower neutron capture cross-section than protium, allowing for the use of unenriched uranium as fuel.

140. Which one of the following statements regarding matter is *not* correc

Which one of the following statements regarding matter is *not* correct ?

[amp_mcq option1=”Matter is anything that occupies space” option2=”At high temperatures matter becomes plasma” option3=”All matter is composed of large particles such as atoms and molecules” option4=”Colloids are made up of larger particles of matter” correct=”option3″]

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UPSC CAPF – 2010
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The statement that is *not* correct regarding matter is “All matter is composed of large particles such as atoms and molecules”.
While atoms and molecules are fundamental building blocks for common states of matter (solid, liquid, gas), not *all* matter is composed *only* of atoms and molecules, especially described as “large particles”. Matter can exist as plasma (ionized gas, consisting of ions and free electrons), which is not composed of intact atoms or molecules. Fundamental particles (like quarks, electrons, neutrinos) are also considered matter. The term “large particles” is also relative and misleading in a fundamental description of matter composition. Statements A, B, and D are correct descriptions of aspects of matter: A) Matter occupies space and has mass. B) Plasma is a high-temperature state of matter. D) Colloids are indeed dispersions of particles larger than those in true solutions.
The four common states of matter are solid, liquid, gas, and plasma. Bose-Einstein condensates are another state of matter at extremely low temperatures. Matter is fundamentally composed of elementary particles, which can combine to form composite particles like protons and neutrons, which in turn form atomic nuclei. Atoms consist of a nucleus and electrons, and atoms combine to form molecules or ionic lattices.
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