Chemistry

291. Which one among the following is present in the nettle leaf hairs that

Which one among the following is present in the nettle leaf hairs that causes burning pain ?

[amp_mcq option1=”Methanoic acid” option2=”Ethanoic acid” option3=”Benzoic acid” option4=”Acetic acid” correct=”option1″]

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Methanoic acid is present in nettle leaf hairs and causes a burning pain.
The stinging hairs (trichomes) of nettle plants contain several irritants, including histamine, acetylcholine, serotonin, and an acid. The primary acid responsible for the burning and stinging sensation is formic acid, also known by its IUPAC name, methanoic acid (HCOOH).
Ethanoic acid is acetic acid (CH₃COOH), found in vinegar. Benzoic acid (C₆H₅COOH) is an aromatic carboxylic acid. While other chemicals contribute, methanoic acid is the key acidic component causing the initial sting.

292. What is the coordination number of Na⁺ and Cl⁻ ions in NaCl lattice ?

What is the coordination number of Na⁺ and Cl⁻ ions in NaCl lattice ?

[amp_mcq option1=”6, 1″ option2=”1, 6″ option3=”6, 6″ option4=”5, 5″ correct=”option3″]

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In the NaCl crystal lattice, both Na⁺ and Cl⁻ ions have a coordination number of 6.
The NaCl crystal structure is a face-centered cubic (FCC) arrangement where each Na⁺ ion is octahedrally surrounded by six Cl⁻ ions, and similarly, each Cl⁻ ion is octahedrally surrounded by six Na⁺ ions.
The coordination number in an ionic lattice refers to the number of oppositely charged ions immediately surrounding a given ion. This coordination number is determined by the relative sizes of the ions and the need to maximize electrostatic attraction while minimizing repulsion.

293. Which one among the following compounds has a sweet and fruity smell ?

Which one among the following compounds has a sweet and fruity smell ?

[amp_mcq option1=”Ethyl alcohol” option2=”Acetic acid” option3=”Ethyl acetate” option4=”Acetophenone” correct=”option3″]

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Ethyl acetate has a sweet and fruity smell.
Esters are a class of organic compounds formed from an alcohol and a carboxylic acid, and they are commonly known for their pleasant, often fruity or flowery odors. Ethyl acetate is an ester derived from ethanol and acetic acid.
Ethyl alcohol (ethanol) has a characteristic alcoholic smell. Acetic acid is a carboxylic acid with a pungent, vinegar-like smell. Acetophenone is a ketone with a sweet, sometimes described as almond-like or floral, smell.

294. Human body works in the pH range of:

Human body works in the pH range of:

[amp_mcq option1=”6.8 – 7.2″ option2=”7.0 – 7.8″ option3=”6.5 – 7.5″ option4=”7.5 – 8.0″ correct=”option2″]

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The human body, particularly blood, maintains a very narrow pH range for proper functioning.
The normal pH range of human blood is slightly alkaline, typically between 7.35 and 7.45. Among the given options, the range of 7.0 – 7.8 is the one that correctly encompasses the typical physiological pH range.
Significant deviations from this narrow pH range can lead to severe health problems. For example, a pH below 7.35 is called acidosis, and a pH above 7.45 is called alkalosis. The body uses buffer systems (like the bicarbonate buffer system) to maintain this delicate pH balance.

295. Water gas is a mixture of:

Water gas is a mixture of:

[amp_mcq option1=”CO₂ and H₂” option2=”CO and H₂” option3=”CO₂ and H₂O” option4=”CO and H₂O” correct=”option2″]

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Water gas is a mixture of carbon monoxide (CO) and hydrogen (H₂).
It is produced by passing steam over red-hot carbon (like coke or coal) at high temperatures (typically 800-1000°C). The reaction is: H₂O(g) + C(s) → CO(g) + H₂(g).
Water gas is a significant industrial fuel and a source of hydrogen. It is also known as synthesis gas or syngas when the ratio of CO to H₂ is adjusted, as it is used in the synthesis of various organic compounds.

296. Which among the following are essential constituents of Portland cemen

Which among the following are essential constituents of Portland cement ?

[amp_mcq option1=”Sand, lime, clay” option2=”Silica, alumina, lime” option3=”Silica, lime, graphite powder” option4=”Sand, graphene, clay” correct=”option2″]

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Portland cement is primarily made from materials containing calcium oxide (lime), silicon dioxide (silica), aluminum oxide (alumina), and iron oxide. The main raw materials are typically limestone (for lime) and clay or shale (for silica, alumina, and iron). These materials are heated in a kiln to produce clinker, which is then ground into fine powder with a small amount of gypsum added. Option B lists Silica, Alumina, and Lime, which are the essential oxide components derived from these raw materials, forming the bulk of the cement clinker.
The major chemical components of Portland cement clinker are tricalcium silicate (alite), dicalcium silicate (belite), tricalcium aluminate (celite), and tetracalcium aluminoferrite (ferrite). These are formed from the reaction of lime (CaO), silica (SiO2), alumina (Al2O3), and iron oxide (Fe2O3) during calcination.
Sand is commonly used as an aggregate in concrete (a mixture of cement, aggregates, and water), but it is not a constituent of cement itself. Graphite powder and graphene are forms of carbon and are not standard components of Portland cement. Clay is a raw material containing silica and alumina, used in cement production, but the essential *constituents* within the clinker are the oxides (silica, alumina, lime, etc.) derived from the raw materials.

297. The relative atomic mass of boron (which exists in two isotopic forms

The relative atomic mass of boron (which exists in two isotopic forms 10B and 11B) is 10·81. What will be the abundance of 10B and 11B, respectively (consider a sample of 100 atoms) ?

[amp_mcq option1=”19% and 81%” option2=”81% and 19%” option3=”38% and 62%” option4=”62% and 38%” correct=”option1″]

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Let the abundance of 10B be x and the abundance of 11B be y. The total abundance is 100%, so x + y = 1 (or 100 if using percentages). The average atomic mass is calculated as the weighted average of the isotopic masses: (mass of 10B * x) + (mass of 11B * y) = Average Atomic Mass. Using approximate integer masses (10 for 10B and 11 for 11B), we have: 10x + 11y = 10.81. Since x + y = 1, we can write y = 1 – x. Substituting this into the equation: 10x + 11(1 – x) = 10.81 => 10x + 11 – 11x = 10.81 => 11 – x = 10.81 => x = 11 – 10.81 = 0.19. So, the abundance of 10B is 0.19 or 19%. Then, y = 1 – x = 1 – 0.19 = 0.81 or 81%. The abundance of 10B and 11B, respectively, is 19% and 81%.
The average atomic mass of an element is the weighted average of the masses of its isotopes, where the weights are their natural abundances. This principle is used to determine the relative abundance of isotopes if the average atomic mass and isotopic masses are known.
Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons, resulting in different atomic masses. Boron’s two stable isotopes are 10B (with 5 protons and 5 neutrons) and 11B (with 5 protons and 6 neutrons). The natural abundance of isotopes is relatively constant for a given element across the Earth.

298. Airbags work on the principle of a chemical reaction triggered by the

Airbags work on the principle of a chemical reaction triggered by the impact producing a gaseous product that causes a sudden volume change. Which one among the following chemical conversions is responsible for this ?

[amp_mcq option1=”Sodium azide into nitrogen gas” option2=”Solid carbon dioxide into gaseous carbon dioxide” option3=”Carbon dioxide into carbon monoxide” option4=”Sudden conversion of gaseous carbon dioxide into carbon monoxide” correct=”option1″]

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Modern automotive airbags typically rely on the rapid decomposition of sodium azide (NaN₃). Upon impact, a sensor triggers an electric current that ignites a small amount of a starter compound, which in turn initiates the decomposition of sodium azide. The chemical reaction is: 2 NaN₃(s) → 2 Na(s) + 3 N₂(g). The large volume of nitrogen gas (N₂) produced rapidly inflates the airbag. Potassium nitrate and silicon dioxide are often included to react with the highly reactive sodium metal produced.
The rapid inflation of an airbag is caused by the generation of a large volume of gas from a chemical reaction triggered by impact. Sodium azide decomposing to nitrogen gas is the basis of this process.
The complete reaction mixture in an airbag contains sodium azide, an oxidizer (like potassium nitrate) to react with the sodium produced, and a substance like silicon dioxide or aluminum oxide to react with the products to form harmless slag. This ensures that no harmful substances are released into the car cabin.

299. Copper sulphate crystals available in the market are blue coloured cry

Copper sulphate crystals available in the market are blue coloured crystals. By careful heating, they turn to white colour. Which one of the following is responsible for the blue colour ?

[amp_mcq option1=”Oxygen” option2=”Nitrogen” option3=”Water” option4=”Hydrogen” correct=”option3″]

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Copper sulphate crystals available in the market are typically copper(II) sulphate pentahydrate (CuSO₄·5H₂O). The blue colour is due to the presence of water molecules coordinated to the copper ions in the crystal lattice. When heated, these crystals lose the water of crystallization, turning into anhydrous copper(II) sulphate (CuSO₄), which is white or off-white. The colour change is a classic demonstration of the role of water of crystallization.
The blue colour of hydrated copper sulphate is caused by the presence of water molecules bound within the crystal structure.
The process of heating hydrated copper sulphate to remove water is an example of dehydration. The reverse process, adding water to anhydrous copper sulphate, will restore the blue colour and is often used as a test for the presence of water. Other metal salts also form coloured hydrates where water of crystallization affects the colour.

300. Which among the following is the correct arrangement of halogens in th

Which among the following is the correct arrangement of halogens in the increasing order of their oxidizing nature ?

[amp_mcq option1=”F, Cl, Br, I” option2=”Cl, Br, F, I” option3=”Br, I, Cl, F” option4=”I, Br, Cl, F” correct=”option4″]

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The oxidizing nature of an element refers to its ability to gain electrons and cause the oxidation of another substance. For halogens (Group 17 elements: F, Cl, Br, I, At), the oxidizing power generally decreases down the group. This is because electronegativity and electron affinity decrease, while the atomic radius increases, making it less favorable to gain an electron as you move from Fluorine to Iodine. Therefore, the increasing order of their oxidizing nature is Iodine (I) < Bromine (Br) < Chlorine (Cl) < Fluorine (F). Fluorine is the strongest oxidizing agent among the halogens.
– Oxidizing nature is the ability to gain electrons.
– For halogens, oxidizing power decreases down the group (from F to I).
– This is due to decreasing electronegativity and electron affinity.
– The order of oxidizing strength is F₂ > Cl₂ > Br₂ > I₂.
– The increasing order of oxidizing nature is I < Br < Cl < F.
Fluorine is the most electronegative element and has a very high oxidizing potential. It can oxidize all other halide ions. Chlorine can oxidize bromide and iodide ions. Bromine can oxidize iodide ions, but not fluoride or chloride ions. Iodine is the weakest oxidizing agent among the common halogens.
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