Chemistry

221. A very large volume of hydrogen can be accommodated by making

A very large volume of hydrogen can be accommodated by making

[amp_mcq option1=”non-metallic hydrides.” option2=”hydrogen peroxide.” option3=”non-stoichiometric hydrides.” option4=”alkali metal hydrides.” correct=”option3″]

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The correct answer is C) non-stoichiometric hydrides.
Certain transition metals (like palladium, titanium, vanadium, etc.) and their alloys can absorb large volumes of hydrogen, forming interstitial (non-stoichiometric) hydrides. In these hydrides, hydrogen atoms occupy interstitial sites within the metal lattice. This property is exploited for hydrogen storage, as these materials can store hydrogen at densities comparable to or even greater than liquid hydrogen, but at less extreme conditions.
Non-metallic hydrides are compounds like water (H2O), ammonia (NH3), etc. Hydrogen peroxide (H2O2) is a chemical compound. Alkali metal hydrides (like NaH, LiH) are ionic hydrides, which react vigorously with water and are not typically used for large-volume, reversible hydrogen storage applications in the same way as interstitial metal hydrides. The ability of metals like palladium to absorb hundreds of times their own volume of hydrogen is a classic example related to non-stoichiometric hydrides.

222. Which one of the following is termed as ‘Dry ice’ ?

Which one of the following is termed as ‘Dry ice’ ?

[amp_mcq option1=”Ice present in ice-cream” option2=”Solid water at Antarctica” option3=”Solid state of carbon dioxide” option4=”Solid water of ionosphere” correct=”option3″]

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‘Dry ice’ is the common name for solid carbon dioxide ($\text{CO}_2$). At standard atmospheric pressure, solid carbon dioxide does not melt into a liquid but instead undergoes sublimation, transitioning directly from the solid phase to the gaseous phase. This is why it is called “dry ice,” as it appears as ice but doesn’t produce liquid water upon warming.
A) Ice present in ice-cream is frozen water.
B) Solid water at Antarctica is frozen water (H₂O ice).
C) Solid state of carbon dioxide is indeed dry ice.
D) Solid water of ionosphere is not a recognized term for dry ice; the ionosphere is a layer of the atmosphere where water exists primarily as gas or plasma, not solid ice.
– Dry ice is solid $\text{CO}_2$.
– Dry ice sublimes (solid to gas transition) at atmospheric pressure.
– Common ice is frozen water (solid H₂O).
Dry ice is much colder than water ice, with a sublimation temperature of -78.5 °C (-109.3 °F) at atmospheric pressure. It is used for cooling, freezing, and fog effects (by causing water vapor in the air to condense).

223. Which one of the following substances is not a mixture ?

Which one of the following substances is not a mixture ?

[amp_mcq option1=”Tin” option2=”Sea water” option3=”Soil” option4=”Air” correct=”option1″]

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Matter can be classified into pure substances (elements and compounds) and mixtures. A mixture is formed when two or more substances are combined physically but not chemically. The components of a mixture retain their individual properties and can often be separated by physical means.
A) Tin (Sn) is a chemical element, found on the periodic table. Elements are pure substances, consisting only of one type of atom. Therefore, tin is not a mixture.
B) Sea water is a solution of various salts (like sodium chloride, magnesium chloride, etc.), dissolved gases, and other substances in water. It is a homogeneous mixture (a solution).
C) Soil is a complex combination of inorganic mineral particles, organic matter, water, air, and living organisms. It is a heterogeneous mixture.
D) Air is a mixture of gases, primarily nitrogen ($\text{N}_2$), oxygen ($\text{O}_2$), argon (Ar), carbon dioxide ($\text{CO}_2$), and trace gases. It is a homogeneous mixture (a solution of gases).
Since Tin is an element and not a combination of different substances physically mixed, it is not a mixture.
– Pure substances include elements and compounds.
– Mixtures are physical combinations of two or more substances.
– Elements cannot be broken down into simpler substances by chemical means.
Elements are the basic building blocks of matter. Compounds are formed by chemical reactions between elements in fixed proportions. Mixtures can have variable compositions. Identifying whether something is a mixture involves checking if it’s a pure element or compound, or a physical blend of multiple substances.

224. Soaps clean surfaces on the principle based on

Soaps clean surfaces on the principle based on

[amp_mcq option1=”Viscosity” option2=”Floatation” option3=”Elasticity” option4=”Surface tension” correct=”option4″]

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Soaps are surfactants, meaning they reduce the surface tension of water. Water molecules have strong cohesive forces, leading to high surface tension. This makes it difficult for water to spread and penetrate fabrics or surfaces. Soaps interfere with these forces, lowering surface tension and allowing water to wet surfaces more effectively. Additionally, soap molecules have a hydrophilic (water-attracting) head and a hydrophobic (oil-attracting) tail. The hydrophobic tails surround grease and dirt particles, forming tiny structures called micelles. These micelles, with their hydrophilic heads facing outwards, are soluble in water and can be easily washed away, carrying the dirt with them. This cleaning action is primarily based on the reduction of surface tension and the emulsification/dispersion of dirt through micelle formation, both consequences of the surfactant properties related to surface tension effects.
– Soaps are surfactants.
– Surfactants reduce the surface tension of water.
– Reduced surface tension allows water to spread and penetrate effectively.
– Soap molecules emulsify grease and dirt by forming micelles.
– The fundamental principle involves the interaction of soap at surfaces (related to surface tension).
Viscosity is the resistance of a fluid to flow. Floatation is based on buoyancy. Elasticity is the ability of a material to return to its original shape after deformation. While these properties exist, they are not the primary principles behind the cleaning action of soaps. The ability to lower surface tension is key to the wetting and emulsification processes central to how soaps remove dirt.

225. Which one of the following does not represent the salt, Calcium carbon

Which one of the following does not represent the salt, Calcium carbonate ?

[amp_mcq option1=”Lime water” option2=”Limestone” option3=”Chalk” option4=”Marble” correct=”option1″]

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Calcium carbonate ($\text{CaCO}_3$) is a common chemical compound found in various natural forms. Limestone, chalk, and marble are all naturally occurring forms of calcium carbonate. Limestone is a sedimentary rock largely composed of calcium carbonate. Chalk is a type of limestone. Marble is a metamorphic rock formed from limestone.
Lime water, however, is a saturated solution of calcium hydroxide ($\text{Ca(OH)}_2$). It is produced by dissolving calcium oxide (quicklime) in water to form calcium hydroxide (slaked lime), and then dissolving the calcium hydroxide in more water. While calcium carbonate can be *formed* by passing carbon dioxide through lime water (causing precipitation), lime water itself is calcium hydroxide solution, not calcium carbonate.
– Calcium carbonate ($\text{CaCO}_3$) exists in forms like limestone, chalk, and marble.
– Lime water is a solution of calcium hydroxide ($\text{Ca(OH)}_2$).
– Passing $\text{CO}_2$ through lime water produces $\text{CaCO}_3$ precipitate.
Calcium carbonate is a widely used substance, for example, as a building material, as an abrasive, in agriculture to reduce soil acidity, and in medicine as an antacid. Calcium hydroxide (lime water) is also used in various industrial processes and as a test for carbon dioxide.

226. A sample of ‘soft soap’ contains

A sample of ‘soft soap’ contains

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

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Soaps are salts of fatty acids. The difference between hard soap and soft soap lies in the cation used. Hard soaps are typically the sodium salts of fatty acids (e.g., derived from NaOH reacting with fat/oil), while soft soaps are typically the potassium salts of fatty acids (e.g., derived from KOH reacting with fat/oil). Therefore, a sample of soft soap contains Potassium.
– Soap is produced by the saponification of fats or oils with a strong alkali.
– Hard soaps use sodium hydroxide (NaOH) as the alkali, resulting in sodium salts of fatty acids.
– Soft soaps use potassium hydroxide (KOH) as the alkali, resulting in potassium salts of fatty acids.
– Soft soaps are generally more soluble in water and produce a richer lather than hard soaps. They are often used in liquid soaps and shaving creams.
– Calcium and Magnesium ions are present in hard water and react with soap to form insoluble precipitates (“soap scum”), which is why soap is less effective in hard water. They are not typically added as components of soap itself.

227. Which one of the following statements about water is not true ?

Which one of the following statements about water is not true ?

[amp_mcq option1=”Hydrogen bonds are present in liquid water.” option2=”Water has a high boiling point.” option3=”Water has a high heat of fusion.” option4=”Water is a non-polar molecule.” correct=”option4″]

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Statement D, “Water is a non-polar molecule”, is not true. Water (H2O) has a bent molecular geometry due to the presence of two lone pairs on the oxygen atom. The O-H covalent bonds are polar because oxygen is more electronegative than hydrogen. Because of the bent shape, the bond dipoles do not cancel out, resulting in a net dipole moment for the entire molecule. Therefore, water is a polar molecule.
– Water is a polar molecule due to its bent structure and polar covalent bonds.
– The polarity and the presence of hydrogen atoms bonded to a highly electronegative oxygen atom enable hydrogen bonding between water molecules.
– Hydrogen bonding is responsible for many of water’s unusual properties, such as high boiling point, high heat of fusion, high specific heat capacity, and high surface tension.
– Statement A is true; hydrogen bonds are extensive in liquid water, forming a dynamic network.
– Statement B is true; water has an exceptionally high boiling point (100°C at 1 atm) compared to other molecules of similar size and molar mass without hydrogen bonding (e.g., H2S, which boils at -60°C).
– Statement C is true; water requires a significant amount of energy to melt (heat of fusion) due to the need to break hydrogen bonds holding the ice lattice together.

228. The raw materials used for the manufacture of Portland cement are

The raw materials used for the manufacture of Portland cement are

[amp_mcq option1=”Lime, silica and sulphur dioxide” option2=”Lime, silica and carbon dioxide” option3=”Lime, silica and alumina” option4=”Lime, silica and boric acid” correct=”option3″]

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The primary raw materials used for the manufacture of Portland cement clinker are calcium oxide (usually derived from limestone or chalk), silicon dioxide (silica, typically from clay or sand), and aluminium oxide (alumina, from clay or bauxite). These materials are mixed in specific proportions, heated in a kiln to high temperatures (calcination and clinkering), and then ground to produce cement. Option C lists lime, silica, and alumina, which are the essential components derived from these raw materials.
– The main chemical components of Portland cement are calcium silicates, calcium aluminates, and calcium ferroaluminates.
– These compounds are formed by heating a mixture of calcareous material (like limestone, source of CaO) and argillaceous material (like clay, source of SiO2 and Al2O3) in a kiln.
– Minor components like iron oxide and gypsum (added during grinding) are also involved but lime, silica, and alumina are the core raw material oxides.
– Limestone (CaCO3) is heated to produce lime (CaO) and carbon dioxide (CO2).
– Clay provides silica (SiO2), alumina (Al2O3), and iron(III) oxide (Fe2O3).
– Sulphur dioxide and boric acid are not standard raw materials for Portland cement. Carbon dioxide is a byproduct of the calcination process, not a raw material that is added.

229. Which one of the following statements about diamond and graphite is no

Which one of the following statements about diamond and graphite is not correct ?

[amp_mcq option1=”Diamond has a tetrahedral structure, whereas graphite has a hexagonal planar structure.” option2=”Both physical and chemical properties of diamond and graphite are different.” option3=”Graphite is soft but diamond is hard.” option4=”Graphite is a good conductor of electricity while diamond is not.” correct=”option2″]

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Statement B, “Both physical and chemical properties of diamond and graphite are different”, is arguably the least accurate or potentially misleading statement compared to the others, which are clear factual distinctions. While their physical properties are vastly different, their chemical properties, stemming from being elemental carbon, share some fundamental similarities (e.g., both combust in oxygen to form CO2, although under different conditions and rates). The difference in chemical reactivity is significant due to their structures, but claiming *all* chemical properties are different might be considered an overstatement in some contexts. Statements A, C, and D are unequivocally correct and describe key differences between diamond and graphite. In competitive exams, if multiple statements are true, the question might hinge on identifying the statement that is not *completely* true or contains a subtle inaccuracy or overgeneralization.
– Diamond and graphite are allotropes of carbon with distinct crystal structures (tetrahedral for diamond, hexagonal planar layers for graphite).
– These structural differences lead to significant differences in physical properties like hardness, density, electrical conductivity, and thermal conductivity.
– While their reactivity differs significantly (graphite is more reactive than diamond), they are both carbon and participate in similar fundamental chemical reactions like combustion.
– Diamond is an electrical insulator and the hardest known natural material.
– Graphite is a good electrical conductor and is soft, used as a lubricant.
– The difference in properties arises from the difference in bonding and structure: sp3 hybridization in diamond forms a rigid 3D network, while sp2 hybridization in graphite forms layers held together by weak van der Waals forces.
– Statement B is considered “not correct” likely because the term “different” might be interpreted as “completely distinct with no commonalities”, which isn’t strictly true for chemical properties as they are both forms of carbon.

230. Which one of the following statements about glass is not correct?

Which one of the following statements about glass is not correct?

[amp_mcq option1=”Glass is often said to be a supercooled liquid.” option2=”Glass has no definite melting point.” option3=”Soda glass is harder than pyrex glass.” option4=”Boron is present in pyrex glass.” correct=”option3″]

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The correct option is C) Soda glass is harder than pyrex glass. This statement is incorrect. Pyrex glass (borosilicate glass) is generally harder and more durable than soda-lime glass (soda glass).
A) Glass is an amorphous solid, lacking a long-range ordered crystalline structure. Its structure is similar to a liquid’s, and it becomes increasingly viscous as it cools, without a sharp transition like freezing. Hence, it is often described as a supercooled liquid or an amorphous solid. This statement is generally considered correct.
B) Due to its amorphous nature, glass does not have a specific melting point. It softens gradually over a range of temperatures. This statement is correct.
C) Soda-lime glass (soda glass) is the most common type of glass (window panes, bottles). Pyrex is a brand of borosilicate glass, which contains boron oxide (B₂O₃) in addition to silica. The addition of boron oxide significantly changes the properties, making it more resistant to thermal shock and chemical corrosion, and generally harder and more resistant to scratches compared to soda-lime glass. Therefore, soda glass is *not* harder than pyrex glass; it is softer.
D) Pyrex glass is a type of borosilicate glass, meaning it contains boron (specifically in the form of boron oxide). This statement is correct.
The composition differences between soda-lime glass and borosilicate glass lead to their different properties. Soda-lime glass typically contains silicon dioxide (silica, ~70%), sodium oxide (soda), and calcium oxide (lime). Borosilicate glass typically contains silica (~80%), boron oxide (~13%), and smaller amounts of sodium oxide and aluminium oxide. The higher silica and boron content contribute to the superior properties of borosilicate glass.
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