Chemistry

181. Liquid vegetable oils are converted to solid margarine by the use of

Liquid vegetable oils are converted to solid margarine by the use of

[amp_mcq option1=”hydrogen gas” option2=”chlorine gas” option3=”carbon dioxide gas” option4=”oxygen gas” correct=”option1″]

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The correct answer is hydrogen gas.
Liquid vegetable oils are typically unsaturated fats, meaning they contain carbon-carbon double bonds. To convert these liquid oils into solid or semi-solid fats like margarine, hydrogen gas is added across the double bonds in the presence of a catalyst (usually nickel, palladium, or platinum). This process is called hydrogenation.
Partial hydrogenation can lead to the formation of trans fats, which have been linked to negative health effects. Modern hydrogenation processes aim to minimize trans fat formation while achieving the desired consistency.

182. Bee sting leaves an acid which causes pain and irritation. The acid re

Bee sting leaves an acid which causes pain and irritation. The acid released is

[amp_mcq option1=”tartaric acid” option2=”citric acid” option3=”ethanoic acid” option4=”methanoic acid” correct=”option4″]

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The correct answer is methanoic acid.
Bee sting venom contains several substances, including formic acid, which is also known as methanoic acid (HCOOH). This acid is primarily responsible for the pain and irritation experienced from a bee sting.
While bee venom contains various components, including peptides and enzymes, formic acid is the key acidic component causing the immediate stinging sensation. Wasp stings, in contrast, are alkaline.

183. Which one of the following salts does not possess water of

Which one of the following salts does not possess water of crystallization?

[amp_mcq option1=”Potassium permanganate” option2=”Blue vitriol” option3=”Washing soda” option4=”Mohr’s salt” correct=”option1″]

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The correct answer is Potassium permanganate.
Salts that do not possess water of crystallization are called anhydrous salts. Among the given options, Potassium permanganate (KMnO₄) is typically an anhydrous salt. Blue vitriol (CuSO₄·5H₂O), Washing soda (Na₂CO₃·10H₂O), and Mohr’s salt ((NH₄)₂Fe(SO₄)₂·6H₂O) are common examples of hydrated salts, meaning they contain a fixed number of water molecules (water of crystallization) associated with their crystal structure.
Water of crystallization is water that is stoichiometrically bound into a crystal. It is necessary for the maintenance of the crystalline properties but can usually be removed by heating, resulting in the anhydrous salt.

184. Bronze is an alloy of

Bronze is an alloy of

[amp_mcq option1=”Cu and Zn” option2=”Cu and Sn” option3=”Zn and Mg” option4=”Fe and Cu” correct=”option2″]

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Bronze is an alloy of copper (Cu) and tin (Sn).
Alloys are mixtures of metals, or a mixture of a metal and another element. Bronze is historically significant and known for its hardness and durability.
Common metal alloys include:
– Brass: Copper (Cu) and Zinc (Zn)
– Bronze: Copper (Cu) and Tin (Sn)
– Stainless Steel: Iron (Fe), Chromium (Cr), Nickel (Ni), and Carbon (C)
– Solder: Tin (Sn) and Lead (Pb)

185. Silver artefacts get tarnished in air due to the formation of

Silver artefacts get tarnished in air due to the formation of

[amp_mcq option1=”silver chloride” option2=”silver oxide” option3=”silver sulphide” option4=”silver sulphate” correct=”option3″]

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Silver artefacts get tarnished in air due to the formation of silver sulphide.
Silver tarnishes when it reacts with sulfur compounds present in the air, such as hydrogen sulfide (H2S). This reaction forms a black layer of silver sulfide (Ag2S) on the surface of the silver.
The reaction is 2Ag(s) + H2S(g) -> Ag2S(s) + H2(g). Tarnishing is accelerated in polluted air or environments with higher concentrations of sulfur gases.

186. Which of the following compounds undergoes/undergo thermal

Which of the following compounds undergoes/undergo thermal decomposition?

[amp_mcq option1=”Zinc oxide” option2=”Silver oxide and zinc oxide” option3=”Silver oxide” option4=”Magnesium oxide” correct=”option3″]

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Silver oxide undergoes thermal decomposition.
Thermal decomposition is the breakdown of a compound by heating. Silver oxide (Ag2O) is relatively unstable and decomposes upon heating into silver metal and oxygen gas (2Ag2O(s) -> 4Ag(s) + O2(g)). Zinc oxide (ZnO) and Magnesium oxide (MgO) are stable oxides that do not decompose easily upon heating under normal conditions.
The ease of thermal decomposition of metal oxides is related to the reactivity of the metal. Oxides of less reactive metals (like silver, mercury, gold) decompose more easily than oxides of more reactive metals (like magnesium, zinc, calcium).

187. To help deep-sea divers breathe, they carry cylinders of oxygen mixed

To help deep-sea divers breathe, they carry cylinders of oxygen mixed with

[amp_mcq option1=”chlorine” option2=”helium” option3=”nitrogen” option4=”ozone” correct=”option2″]

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To help deep-sea divers breathe, they carry cylinders of oxygen mixed with helium.
At high pressures experienced during deep-sea dives, the nitrogen in air can cause nitrogen narcosis, which impairs judgment and coordination. Oxygen at high partial pressures can also become toxic. To avoid these issues, the breathing gas mixture often replaces nitrogen with helium, which is less narcotic and also less dense than nitrogen, making breathing easier at depth. This mixture of oxygen and helium is called Heliox.
Other gas mixtures like Trimix (oxygen, helium, and nitrogen) are also used depending on the depth and duration of the dive. Chlorine and ozone are toxic gases and would not be used in breathing mixtures.

188. Which one of the following solutions is not capable of conducting

Which one of the following solutions is not capable of conducting electricity?

[amp_mcq option1=”Copper sulphate” option2=”Sodium chloride” option3=”Sugar” option4=”Sodium hydroxide” correct=”option3″]

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Sugar solution is not capable of conducting electricity.
For a solution to conduct electricity, it must contain free-moving ions. Solutions of ionic compounds (like Copper sulphate, Sodium chloride, Sodium hydroxide) dissociate into ions when dissolved in water, allowing them to conduct electricity. Sugar (sucrose) is a covalent compound; when it dissolves in water, it remains as neutral molecules and does not produce ions.
Electrolytes are substances that produce ions when dissolved in a solvent, making the solution electrically conductive. Non-electrolytes, like sugar, dissolve but do not ionize, and their solutions do not conduct electricity.

189. Which one of the following metals floats in cold water?

Which one of the following metals floats in cold water?

[amp_mcq option1=”Magnesium” option2=”Calcium” option3=”Potassium” option4=”Copper” correct=”option3″]

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Potassium is a metal that floats in cold water.
Metals less dense than water (density < 1 g/cm³) and which react with water tend to float. Potassium (density ~0.89 g/cm³) and Sodium (density ~0.97 g/cm³) are alkali metals that are less dense than water and react vigorously with cold water, producing hydrogen gas which aids flotation. Calcium (density ~1.55 g/cm³) is denser than water but reacts with cold water, and the hydrogen bubbles produced stick to its surface, causing it to float temporarily. Magnesium and Copper do not react with cold water in a way that causes them to float.
Highly reactive metals like Potassium and Sodium react exothermically with cold water to form hydroxides and hydrogen gas. This reaction can be quite vigorous. While Calcium also reacts with cold water and floats, Potassium and Sodium are well-known examples of metals that float and move rapidly on the surface during the reaction. Among the options provided, Potassium is the most definitive answer for a metal that floats in cold water due to its low density and vigorous reaction.

190. Which one of the following is the correct reactivity series with

Which one of the following is the correct reactivity series with water?

[amp_mcq option1=”Zinc > Iron > Lead > Copper” option2=”Copper > Lead > Zinc > Iron” option3=”Copper > Zinc > Iron > Lead” option4=”Zinc > Copper > Iron > Lead” correct=”option1″]

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The correct reactivity series with water among the given metals is Zinc > Iron > Lead > Copper.
The reactivity series lists metals in order of decreasing reactivity. Metals higher in the series are more reactive. In the given options, Zinc is more reactive than Iron, which is more reactive than Lead, which is more reactive than Copper.
Highly reactive metals like Potassium and Sodium react vigorously with cold water. Moderately reactive metals like Magnesium and Zinc react with hot water or steam. Less reactive metals like Iron, Lead, Copper, Silver, and Gold do not react with water or steam under normal conditions, or react very slowly (like Iron rusting in the presence of water and oxygen). The general order of reactivity involving water reaction is K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Ag > Au. Comparing the given metals (Zn, Fe, Pb, Cu) shows the order Zn > Fe > Pb > Cu.
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