Chemistry

161. Which among the following statements with respect to carbon is/are cor

Which among the following statements with respect to carbon is/are correct ?

  • 1. Carbon forms the basis for all living organisms and many things we use
  • 2. Carbon shows tetra-valency and the property of catenation
  • 3. Carbon forms covalent bonds with itself and other elements
  • 4. Carbon forms compounds containing triple and tetra bonds between carbon atoms

Select the correct answer using the code given below :

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

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Statements 1, 2, and 3 are correct. Carbon forms the backbone of all organic life and is present in countless materials we use (statement 1). Carbon has four valence electrons, allowing it to form four covalent bonds (tetra-valency), and it can bond with itself to form long chains or rings (catenation) (statement 2). Carbon forms covalent bonds not only with itself but also with other elements like hydrogen, oxygen, nitrogen, etc. (statement 3). Statement 4 is incorrect; carbon forms single, double, and triple bonds with other carbon atoms but not stable tetra (quadruple) bonds in typical organic chemistry contexts.
Carbon’s unique properties of tetra-valency and catenation, and its ability to form strong covalent bonds, are fundamental to organic chemistry and the diversity of carbon compounds. Carbon forms single, double, and triple bonds, but not quadruple bonds, between carbon atoms in stable molecules.
The vast number of carbon compounds makes organic chemistry a distinct branch of chemistry. Catenation is particularly strong in carbon, enabling the formation of complex molecular structures. While theoretical studies have explored the possibility of quadruple bonds in some exotic carbon species, they are not characteristic of carbon bonds in everyday substances.

162. As proposed by Dalton, which of the following symbol represents phosph

As proposed by Dalton, which of the following symbol represents phosphorus ?

[amp_mcq option1=”Circle with P inside” option2=”Circle with L inside” option3=”Circle with vertical and horizontal lines crossing in the center” option4=”Circle with three lines radiating from the center to the circumference” correct=”option4″]

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As proposed by Dalton in his atomic theory, each element had a unique symbol. Phosphorus was represented by a circle with three lines radiating outwards from the center to the circumference.
Dalton’s symbols were pictorial representations of elements and compounds, unlike the modern alphabetical symbols.
Other examples of Dalton’s symbols include a simple circle for Oxygen, a circle with a dot in the center for Hydrogen, and a circle with vertical and horizontal lines crossing for Sulphur (often shown as + inside circle or vertical/horizontal lines). Option A represents the modern symbol for Phosphorus inside a circle, which was not Dalton’s representation.

163. Kerosene and petrol mixture can be best separated by

Kerosene and petrol mixture can be best separated by

[amp_mcq option1=”Sublimation” option2=”Separating funnel” option3=”Fractional distillation” option4=”Compressing and cooling” correct=”option3″]

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The correct method to separate a mixture of kerosene and petrol is fractional distillation. Both kerosene and petrol are miscible liquids with different boiling points (petrol boils roughly between 40°C and 205°C, kerosene between 175°C and 325°C). Fractional distillation is used to separate miscible liquids that have close boiling points.
Fractional distillation is a technique used to separate miscible liquids with different boiling points, involving repeated vaporization and condensation steps within a fractionating column.
Sublimation is used for separating a solid that sublimes from a non-subliming solid or a liquid. A separating funnel is used to separate immiscible liquids. Compressing and cooling is a method used to liquefy gases.

164. Which among the following is NOT true with respect to colloidal soluti

Which among the following is NOT true with respect to colloidal solution ?

[amp_mcq option1=”Particles are uniformly distributed throughout the solution” option2=”Colloidal solution is homogenous in nature” option3=”They show Tyndal effect” option4=”They do not settle down when kept undisturbed” correct=”option2″]

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The statement “Colloidal solution is homogenous in nature” is NOT true.
Colloidal solutions are fundamentally heterogeneous mixtures. Although they may appear homogeneous to the naked eye because the dispersed particles do not settle out, they are heterogeneous at the microscopic level.
Properties of colloidal solutions include: they are heterogeneous; the particle size is larger than in true solutions but smaller than in suspensions (typically 1 nm to 1 $\mu$m); they exhibit the Tyndall effect (scattering of light); they undergo Brownian motion; they are generally stable and do not settle down when left undisturbed; they often carry an electric charge. Statement A is also generally not strictly true in the sense of uniform distribution like a true solution, but B is the most definitive and fundamental falsehood about the nature of colloids.

165. Which one of the following metals can be extracted using carbon as red

Which one of the following metals can be extracted using carbon as reducing agent ?

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

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Zinc can be extracted using carbon as a reducing agent.
Metals less reactive than carbon can be extracted from their oxides by reduction with carbon (smelting). In the reactivity series, carbon is more reactive than zinc, silver, and gold, but less reactive than aluminium. Therefore, oxides of zinc, silver, and gold can potentially be reduced by carbon, while aluminium oxide cannot.
Aluminium is extracted by electrolysis of molten aluminium oxide (alumina) using the Hall-Héroult process because it is much more reactive than carbon. Zinc is commonly extracted from its oxide ($\text{ZnO}$) by heating it with carbon in a process called smelting: $\text{ZnO} + \text{C} \rightarrow \text{Zn} + \text{CO}$. Silver and gold are often found in native states or extracted using processes like cyanidation or from sulfide ores, although carbon can be involved in some extraction stages for silver, zinc is a clearer example of direct oxide reduction by carbon among the options.

166. 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
(Process)		 List II
(Separation method)
A. Separation of acetone and water from their mixture 1. Chromatography
B. Separation of water and kerosene oil from their mixture 2. Centrifugation
C. Separation of cream from milk 3. Distillation
D. Separation of pigments from plant extract 4. Separating Funnel

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

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C) The correct matching is A-3, B-4, C-2, D-1.
– This question requires matching separation processes with appropriate methods based on the properties of the mixtures and their components.
– A. Separation of acetone and water from their mixture: Acetone and water are miscible liquids with different boiling points. Distillation is used to separate miscible liquids based on differences in volatility. Acetone boils at a lower temperature (around 56°C) than water (100°C), allowing it to be vaporized and condensed separately. This matches with 3. Distillation.
– B. Separation of water and kerosene oil from their mixture: Water and kerosene oil are immiscible liquids with different densities. They form two distinct layers when left undisturbed. A separating funnel is used to separate immiscible liquids, allowing the denser liquid (water) to be drained out from the bottom. This matches with 4. Separating Funnel.
– C. Separation of cream from milk: Milk is a suspension or emulsion of fat globules (cream) in a watery phase. Centrifugation is used to separate components of a mixture based on density differences using centrifugal force. Spinning milk rapidly forces the denser skim milk to the periphery while the lighter cream concentrates towards the center. This matches with 2. Centrifugation.
– D. Separation of pigments from plant extract: Plant extracts contain a mixture of different colored pigments. Chromatography is a technique used to separate components of a mixture based on their differential partitioning between a stationary phase and a mobile phase. Different pigments travel at different rates, allowing them to be separated. This matches with 1. Chromatography.
– Distillation is used for miscible liquids with different boiling points.
– Separating funnel is used for immiscible liquids.
– Centrifugation is used to separate components based on density differences, often for solid-liquid suspensions or liquid-liquid emulsions.
– Chromatography is a versatile technique for separating components based on differential affinities to stationary and mobile phases, widely used for separating colored substances (pigments).

167. Which one of the following metal is NOT an essential component in stai

Which one of the following metal is NOT an essential component in stainless steel ?

[amp_mcq option1=”Iron” option2=”Nickel” option3=”Chromium” option4=”Tin” correct=”option4″]

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D) Tin is NOT an essential component in stainless steel.
– Stainless steel is primarily an alloy based on Iron (Fe).
– The key element that provides its characteristic corrosion resistance (“stainless” property) is Chromium (Cr), which must be present in a minimum amount (typically 10.5% by mass). Chromium forms a passive, protective oxide layer on the surface.
– Nickel (Ni) is another common and essential alloying element in many widely used types of stainless steel, particularly austenitic stainless steels (like the 300 series, e.g., 304 and 316). Nickel enhances corrosion resistance, strength, and ductility.
– Iron, Chromium, and often Nickel are the primary essential metallic components of stainless steel. Other elements like Carbon (controlled for strength and ductility), Manganese, Silicon, Molybdenum (for increased corrosion resistance), etc., are also present, but Iron, Chromium, and Nickel are central to its structure and properties.
– Tin (Sn) is not typically used as an alloying element in stainless steel. It is used in other alloys (like bronze, pewter, solder) or as a coating (tin plating), but it is not considered an essential component of stainless steel formulations.

168. What is the action of litmus on ethanol ?

What is the action of litmus on ethanol ?

[amp_mcq option1=”Litmus is neutral towards ethanol” option2=”Ethanol turns blue litmus to red; confirming acidic nature of ethanol” option3=”Ethanol turns red litmus to blue; confirming basic nature of ethanol” option4=”Ethanol decolorizes litmus through bleaching action” correct=”option1″]

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A) Litmus is neutral towards ethanol.
– Litmus is an acid-base indicator. It turns red in acidic solutions (pH < 7) and blue in basic solutions (pH > 7).
– Ethanol (C₂H₅OH) is an alcohol. The -OH group in alcohols is covalently bonded, unlike the ionic hydroxide in strong bases (e.g., NaOH).
– Alcohols are generally considered neutral compounds in aqueous solutions. While they can act as very weak acids (donating a proton from the -OH group, especially when reacting with strong bases like alkali metals) or very weak bases (accepting a proton from a strong acid at the oxygen atom), their acidity or basicity is negligible in the context of affecting litmus paper pH indicators.
– Ethanol does not dissociate significantly in water to produce H⁺ ions (acidic) or OH⁻ ions (basic).
– Therefore, when litmus paper is placed in ethanol or an aqueous solution of ethanol, its color remains unchanged (red litmus stays red, blue litmus stays blue), indicating a neutral pH.
– Ethanol does not possess bleaching properties like chlorine-based compounds.

169. Which one of the following acid is used by goldsmith for cleaning of g

Which one of the following acid is used by goldsmith for cleaning of gold and silver articles ?

[amp_mcq option1=”Sulphuric acid” option2=”Nitric acid” option3=”Hydrochloric acid” option4=”Phosphoric acid” correct=”option2″]

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B) Nitric acid is commonly used by goldsmiths for cleaning gold and silver articles.
– Goldsmiths often need to clean gold and silver items to remove tarnish, dirt, and oxidation.
– Tarnish on silver is typically silver sulfide (Ag₂S), and tarnish on gold can involve sulfides or oxides depending on the alloy.
– Nitric acid (HNO₃) is effective in dissolving many metal oxides and sulfides, including silver sulfide tarnish, while not significantly affecting the noble metals like gold and pure silver (though alloys might react).
– Hydrochloric acid (HCl) can also be used for cleaning certain metal surfaces but is less effective against silver sulfide than nitric acid.
– Sulphuric acid (H₂SO₄) is a strong acid but not typically preferred for cleaning jewellery tarnish compared to nitric or hydrochloric acid.
– Phosphoric acid (H₃PO₄) is a weaker acid used in some cleaning agents (like rust removers) but not commonly by goldsmiths for gold and silver tarnish.
– A mixture of concentrated nitric acid and concentrated hydrochloric acid (in a 1:3 ratio), known as Aqua Regia, is capable of dissolving gold and platinum. This is used for refining or testing gold, NOT for cleaning finished jewellery.

170. Which one of the following is NOT an example of organic compound ?

Which one of the following is NOT an example of organic compound ?

[amp_mcq option1=”Ammonium cyanate” option2=”Marsh gas” option3=”Urea” option4=”Cane sugar” correct=”option1″]

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A) Ammonium cyanate is NOT an example of an organic compound.
– Organic compounds are generally defined as compounds containing carbon, especially those with C-H bonds. They typically originate from biological sources or contain carbon in combination with hydrogen, oxygen, nitrogen, sulfur, etc.
– There are exceptions to the “contains carbon” rule for inorganic compounds, which include oxides of carbon (CO, CO₂), carbonates, bicarbonates, cyanides, cyanates, thiocyanates, carbides, and elemental carbon forms.
– Ammonium cyanate (NH₄OCN) is an ionic salt formed from the ammonium ion (NH₄⁺) and the cyanate ion (OCN⁻). It is classified as an inorganic salt. Historically, it is famous because Friedrich Wöhler synthesized urea (an organic compound) from it in 1828, which was a significant step in disproving the vital force theory.
– Marsh gas is Methane (CH₄), a simple hydrocarbon (alkane) and a classic organic compound.
– Urea ((NH₂)₂CO) contains a carbonyl group (C=O) and amine groups (NH₂). It is an organic compound, specifically an amide.
– Cane sugar is Sucrose (C₁₂H₂₂O₁₁), a disaccharide carbohydrate, which is a large class of organic compounds.
– Therefore, Ammonium cyanate is the only compound in the list that is considered inorganic.
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