Chemistry

321. Which one of the following is a covalent compound?

Which one of the following is a covalent compound?

[amp_mcq option1=”Calcium oxide” option2=”Sodium nitride” option3=”Silicon carbide” option4=”Zinc sulphide” correct=”option3″]

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Among the given options, Silicon carbide (SiC) is predominantly a covalent compound.
Covalent compounds are formed by the sharing of electrons between atoms, typically non-metals or metalloids. Ionic compounds are formed by the transfer of electrons between a metal and a non-metal, resulting in the formation of ions held together by electrostatic attraction.
Calcium oxide (CaO), Sodium nitride (Na₃N), and Zinc sulphide (ZnS) are compounds formed between a metal and a non-metal. While ZnS has some covalent character, CaO and Na₃N are strongly ionic. SiC is a ceramic material where silicon and carbon atoms are bonded covalently in a crystal lattice structure, forming a giant covalent network.

322. Which one of the following is the correct molecular formula of ammoniu

Which one of the following is the correct molecular formula of ammonium carbonate if the valency of ammonium ion is (+1) and carbonate anion is (-2) ?

[amp_mcq option1=”(NH₄)₂CO₃” option2=”NH₄(CO₃)₂” option3=”(NH₃)₂CO₃” option4=”NH₄CO₃” correct=”option1″]

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To form a neutral compound, the total positive charge from the cations must balance the total negative charge from the anions. Given the valencies, the correct ratio of ammonium ions to carbonate ions needs to be determined.
The valency (or charge) of the ammonium ion (NH₄⁺) is +1. The valency (or charge) of the carbonate anion (CO₃²⁻) is -2. To form a neutral compound, we need a total positive charge equal in magnitude to the total negative charge. If we take two ammonium ions, the total positive charge is 2 * (+1) = +2. If we take one carbonate ion, the total negative charge is 1 * (-2) = -2. The charges +2 and -2 balance to give a neutral compound. Therefore, the formula is (NH₄)₂CO₃, indicating two ammonium ions for every one carbonate ion.
When writing formulas for ionic compounds, the cation is written first, followed by the anion. Subscripts indicate the number of ions required to achieve charge neutrality. If the ion is polyatomic (like NH₄⁺ or CO₃²⁻) and more than one is needed, the ion formula is enclosed in parentheses before the subscript.

323. Which one of the following is a chemical change?

Which one of the following is a chemical change?

[amp_mcq option1=”Dissolving sugar in water” option2=”Melting of ice” option3=”Crystallization” option4=”Milk turning sour” correct=”option4″]

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A chemical change involves the formation of new substances with different chemical properties. Milk turning sour is a process where lactose is converted into lactic acid by bacteria, resulting in a change in chemical composition.
Physical changes alter the form or appearance of a substance but not its chemical identity (e.g., dissolving, melting, freezing, boiling, crystallization). Chemical changes result in the formation of one or more new substances with different chemical properties (e.g., burning, rusting, cooking, souring of milk).
Dissolving sugar in water, melting of ice, and crystallization are all physical changes. In milk turning sour, bacteria perform fermentation, converting lactose (a sugar) into lactic acid, which changes the taste and properties of the milk. This is a clear example of a chemical reaction producing new substances.

324. Refining of petroleum is carried out using which one of the following

Refining of petroleum is carried out using which one of the following techniques?

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

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Refining of petroleum (crude oil) is done by separating its various components based on their different boiling points. This process is called fractional distillation.
Crude oil is a complex mixture of hydrocarbons with varying chain lengths and boiling points. Fractional distillation involves heating the crude oil and separating the vapours into different fractions at various levels of a fractionating column based on their condensation temperatures. Lighter fractions with lower boiling points rise higher in the column, while heavier fractions with higher boiling points condense lower down.
Evaporation is used to separate a solvent from a non-volatile solute. A separating funnel is used to separate immiscible liquids. Sublimation is used to separate a substance that changes directly from solid to gas from substances that do not sublime. Fractional distillation is the standard industrial method for separating crude oil into useful products like gasoline, diesel, kerosene, etc.

325. Which one of the following is not a solution?

Which one of the following is not a solution?

[amp_mcq option1=”Alloy” option2=”Milk” option3=”Air” option4=”Sugar” correct=”option2″]

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A solution is a homogeneous mixture of two or more substances. Among the given options, milk is a heterogeneous mixture (specifically a colloid).
An alloy is a homogeneous mixture of metals or a metal and a non-metal (e.g., brass, steel), so it is a solution (solid solution). Air is a homogeneous mixture of gases (primarily nitrogen and oxygen), so it is a solution (gaseous solution). Milk contains dispersed particles of fat and protein which are not uniformly distributed at the microscopic level, making it a heterogeneous mixture (colloid). Sugar itself is a pure substance (compound), but if dissolved in water, it forms a homogeneous mixture (sugar solution). However, given the options as listed, Milk is the only one that is definitively not a solution.
Mixtures can be homogeneous (solutions) or heterogeneous (suspensions and colloids). Solutions have uniform composition throughout. Colloids have particles dispersed uniformly, but these particles are larger than molecules and cause light scattering (Tyndall effect); they are considered heterogeneous. Suspensions have even larger particles that settle out over time.

326. Common salt (NaCl) is not used as a raw material for preparation of

Common salt (NaCl) is not used as a raw material for preparation of which one of the following compounds?

[amp_mcq option1=”Bleaching powder” option2=”Baking soda” option3=”Plaster of Paris” option4=”Washing soda” correct=”option3″]

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The correct answer is (C) Plaster of Paris.
Plaster of Paris (Calcium sulfate hemihydrate, CaSO4·½H2O) is produced by heating gypsum (Calcium sulfate dihydrate, CaSO4·2H2O) to about 150°C. The main raw material for Plaster of Paris is gypsum.
Common salt (NaCl) is a key raw material for the production of:
– Bleaching powder: Chlorine gas, used to make bleaching powder, is typically produced by electrolysis of brine (aqueous NaCl).
– Baking soda (NaHCO3) and Washing soda (Na2CO3): Both are primarily manufactured using the Solvay process, which utilizes brine (NaCl solution), ammonia, and carbon dioxide.
Thus, NaCl is a raw material (directly or indirectly) for bleaching powder, baking soda, and washing soda, but not for Plaster of Paris.

327. Reaction of quick lime (CaO) with water to produce slaked lime (Ca(OH)

Reaction of quick lime (CaO) with water to produce slaked lime (Ca(OH)₂) is an example of

[amp_mcq option1=”Displacement reaction.” option2=”Endothermic reaction.” option3=”Decomposition reaction.” option4=”Exothermic reaction.” correct=”option4″]

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The reaction between quick lime (calcium oxide, CaO) and water (H₂O) to form slaked lime (calcium hydroxide, Ca(OH)₂) is represented by the equation: CaO(s) + H₂O(l) → Ca(OH)₂(s). This reaction is well-known for releasing a significant amount of heat, making it a highly exothermic process.
Exothermic reactions are chemical reactions that release energy, typically in the form of heat or light. Endothermic reactions absorb energy. Displacement reactions involve one element displacing another from a compound. Decomposition reactions involve a single compound breaking down into simpler substances. The reaction of quick lime with water fits the definition of an exothermic reaction due to the large heat release, also sometimes classified as a combination reaction.
This reaction is used in the industrial production of slaked lime, which has various applications, including in mortar and plaster, water treatment, and agriculture. The heat released during the reaction is often sufficient to boil the water.

328. Which one of the following acids is predominantly found in tomatoes ?

Which one of the following acids is predominantly found in tomatoes ?

[amp_mcq option1=”Acetic acid” option2=”Tartaric acid” option3=”Oxalic acid” option4=”Lactic acid” correct=”option3″]

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Tomatoes contain several organic acids, including citric acid, malic acid, and oxalic acid. While citric acid is often the most abundant overall acid, tomatoes are a particularly significant source of oxalic acid compared to many other common fruits and vegetables. Among the options provided, oxalic acid is the predominant one found in notable quantities in tomatoes.
Oxalic acid is a dicarboxylic acid (COOH-COOH) found in many plants. Acetic acid is the primary component of vinegar. Tartaric acid is found in grapes and tamarind. Lactic acid is produced during fermentation (e.g., in yogurt) and in muscles during strenuous exercise.
The presence of oxalic acid contributes to the tangy taste of tomatoes. While important for understanding nutritional content and potential interactions (like with calcium), it’s worth noting that the relative abundance of acids can vary slightly depending on the tomato variety and ripeness.

329. Which one of the following reactions does not result in the evolutio

Which one of the following reactions does not result in the evolution of hydrogen gas ?

[amp_mcq option1=”Reaction of zinc metal with dilute sulphuric acid solution” option2=”Mixing water to Plaster of Paris” option3=”Heating zinc metal with sodium hydroxide solution” option4=”Reaction of potassium metal with water” correct=”option2″]

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Mixing water with Plaster of Paris (Calcium sulfate hemihydrate, CaSO₄·½H₂O) results in a hydration reaction where water is absorbed to form gypsum (Calcium sulfate dihydrate, CaSO₄·2H₂O). This reaction is exothermic and causes the mixture to set and harden, but it does not produce any gas, including hydrogen.
The reactions in options A, C, and D all involve the liberation of hydrogen gas:
A) Active metals like zinc react with dilute acids (Zn + H₂SO₄ → ZnSO₄ + H₂).
C) Amphoteric metals like zinc react with strong bases upon heating (Zn + 2NaOH → Na₂ZnO₂ + H₂).
D) Highly reactive metals like potassium react vigorously with water (2K + 2H₂O → 2KOH + H₂).
Plaster of Paris is commonly used in construction, casting, and medical applications (like casts for broken bones) due to its ability to quickly set after mixing with water. The setting process involves the crystallization of gypsum.

330. Which one of the following materials is not an allotrope of carbon ?

Which one of the following materials is not an allotrope of carbon ?

[amp_mcq option1=”Diamond” option2=”Graphene” option3=”Fly ash” option4=”Fullerene” correct=”option3″]

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Fly ash is a residue produced from the combustion of pulverized coal in thermal power plants. It is primarily composed of fine particles of various oxides and minerals, such as silicon dioxide (SiO₂), aluminium oxide (Al₂O₃), iron oxide (Fe₂O₃), and calcium oxide (CaO), along with some unburnt carbon. It is not a pure form of carbon existing in a specific structural modification like diamond, graphene, or fullerene.
Allotropes are different forms of the same element in the same physical state. Carbon exists in many allotropic forms due to its ability to bond in various ways. Common allotropes include diamond (tetrahedral sp³ bonding), graphite (layered sp² bonding), graphene (single layer of graphite), fullerenes (spherical or elliptical sp² bonding, like C₆₀), carbon nanotubes, and lonsdaleite.
Fly ash is often used as a pozzolanic material in concrete mixtures, improving its properties. While it contains some unburnt carbon, its composition is complex and includes many non-carbon components, classifying it as an industrial byproduct rather than an allotrope of carbon.
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