▶️ Answer/Explanation
Room temperature is generally considered to be around 25°C. For a substance to exist as a gas at room temperature, its boiling point must be lower than 25°C, meaning it has already fully vaporized. Looking at the provided table, only element A has a boiling point (−35°C) that is below room temperature. Elements B, C, and D all have boiling points above 25°C, so they would still remain in either a liquid or solid state at room temperature.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
In a pure solid, the constituent particles are tightly packed together in a highly ordered, regular three-dimensional lattice structure, which corresponds to statement 1. Because of strong intermolecular forces holding them in place, these particles cannot move freely over one another like they do in a liquid; instead, they simply vibrate about their fixed positions, which aligns with statement 4. Statements 2 and 3 describe the random arrangement and translational movement characteristic of liquids and gases. Thus, only statements 1 and 4 accurately describe the solid state.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
The nucleon number, also known as the mass number, represents the total number of protons and neutrons located inside the nucleus of an atom. In this given atom, there are 12 protons and 13 neutrons, which combine to give a total of 25 nucleons (12 + 13 = 25). Electrons orbit outside the central nucleus and are not classified as nucleons, meaning they are excluded from this total.
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
The particle diagram depicts two distinct molecular chemical structures distributed among four total components, where each individual particle is a molecule made up of more than one type of atom bonded together. Since a molecule with different bonded elements represents a compound, the system is classified as a heterogeneous collection containing exactly two separate chemical compounds. This eliminates the options containing elements because no pure singular atom groups or molecules of matching atoms are isolated, and it eliminates the option of four distinct compounds since pairs of the structures match each other identically.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
During the reaction, each metallic sodium atom transfers its single valence electron to a non-metallic chlorine atom to achieve a stable octet structure. By giving away a negatively charged electron, the neutral sodium atom gets oxidized and transforms into a positively charged ion, which is specifically called a cation ($Na^{+}$). Conversely, the chlorine atom gains that electron to become a negatively charged chloride anion ($Cl^{-}$), setting up an electrostatic attraction that yields sodium chloride.
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
Nitrogen monoxide is a simple molecular compound, meaning its structure consists of discrete molecules held together by weak intermolecular forces. Because these weak forces require very little thermal energy to overcome, the compound has a low boiling point. Additionally, simple molecular substances do not have free-moving electrons or mobile ions available to carry an electric charge. As a result, nitrogen monoxide exhibits poor electrical conductivity, perfectly matching the properties listed in row D.
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
Because element X is located in Group II of the Periodic Table, its atoms contain two valency electrons and form stable cations with a $+2$ charge ($X^{2+}$). When reacting with a sulfate ion ($SO_{4}^{2-}$), they combine in a $1:1$ ratio to create the neutral salt $XSO_{4}$ alongside hydrogen gas ($H_{2}$), ruling out options C and D. Similarly, during combustion, the $X^{2+}$ cation pairs up with a oxide anion ($O^{2-}$) to yield a basic oxide with the empirical chemical formula $XO$, which makes option A the correct row.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
To find the relative molecular mass (Mr) of sulfuric acid (H2SO4), we must sum the relative atomic masses of all atoms present in its chemical formula. According to the Periodic Table, the relative atomic mass of Hydrogen is 1, Sulfur is 32, and Oxygen is 16. Calculating the total mass gives us (2 × 1) + (1 × 32) + (4 × 16) = 2 + 32 + 64 = 98. Therefore, the relative molecular mass of sulfuric acid is exactly 98, making the last option the correct choice.
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
According to the balanced chemical equation, $1\text{ mol}$ of nitrogen gas ($M_r = 28$) reacts completely to produce $2\text{ mol}$ of ammonia ($M_r = 17$). This stoichiometric relationship means that $28\text{ tonnes}$ of nitrogen will always yield $34\text{ tonnes}$ of ammonia ($2 \times 17$). By setting up a direct mass proportion ($\frac{28}{34} = \frac{x}{51}$), solving for $x$ reveals that exactly $42\text{ tonnes}$ of nitrogen gas are needed to generate $51\text{ tonnes}$ of ammonia.
✅ Answer: (C)
✅ Answer: (C)
▶️ Answer/Explanation
In electroplating, the object to be plated must be connected as the negative electrode (cathode) so that positively charged metal ions from the solution can gain electrons and deposit onto its surface. The positive electrode (anode) is made of the pure plating metal (silver), which dissolves into the solution to continuously replace the deposited ions. Therefore, the electrolyte must be a soluble salt of the plating metal, such as aqueous silver nitrate, to maintain a steady concentration of silver ions in the bath.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
During the electrolysis of concentrated aqueous sodium chloride, chlorine gas forms at the positive anode while hydrogen gas is evolved at the negative cathode. When dilute sulfuric acid undergoes electrolysis, oxygen gas is liberated at the anode and hydrogen gas is released at the cathode. Consequently, both solutions generate gaseous products at both electrodes (making Statement 1 correct) and specifically produce hydrogen gas at their respective cathodes (making Statement 3 correct).
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
An endothermic reaction takes in thermal energy from the surroundings. Because energy is absorbed, the products are at a higher energy level than the reactants. On a reaction pathway diagram, this is shown by a curve that starts lower at the reactants and finishes higher at the products. Diagram B correctly illustrates this upward slope, indicating a positive enthalpy change typical of an endothermic process.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
When a match is struck, friction provides the initial activation energy required to start the reaction, but once burning, the reaction releases significant amounts of thermal and light energy. Chemical reactions that transfer thermal energy to their surroundings, causing an overall release of heat, are classified as exothermic. Therefore, the chemical reaction of a burning match is exothermic because energy is given out to the surroundings.
✅ Answer: (C)
✅ Answer: (C)
▶️ Answer/Explanation
Manganese(IV) oxide operates as a catalyst, meaning it successfully increases the overall rate of chemical decomposition by lowering the necessary activation energy (making Statement 1 correct). Because a catalyst remains chemically unaltered by the process, its chemical composition and total mass are completely preserved from start to finish (making Statement 3 correct). However, a catalyst can never alter the ultimate yield or maximum volume of oxygen produced, as the final amount of product is strictly determined by the initial quantity of hydrogen peroxide reactant available (making Statement 2 incorrect).
✅ Answer: (C)
✅ Answer: (C)
▶️ Answer/Explanation
To determine the highest average rate of reaction, calculate the rate of gas production by dividing the volume of gas collected by the time taken for each student. Option A yields a rate of 0.75 cm3/s, Option B yields 1.25 cm3/s, Option C yields approximately 0.94 cm3/s, and Option D yields 0.90 cm3/s. Comparing these values, Option B demonstrates the highest rate of reaction at 1.25 cm3/s, regardless of the total overall volume of gas collected.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
By definition, a redox process is characterized as a chemical reaction where both reduction and oxidation take place simultaneously[cite: 446, 447]. In this specific mechanism, hydrogen atoms undergo oxidation by gaining oxygen and losing electrons to shift from an oxidation state of 0 to +1[cite: 448, 452, 454]. Concurrently, oxygen molecules experience reduction by losing their uncombined elemental status and gaining electrons to transition from 0 to a -2 state, confirming that option A is the correct answer[cite: 455, 458, 459].
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
Ethanoic acid is a carbon-containing molecule, classifying it as an organic compound (Statement 2). Because it only partially dissociates in aqueous solutions, it is a weak acid that maintains an acidic pH below 7 (ruling out Statement 1) and shifts universal indicator paper to an orange-yellow shade (Statement 3). Finally, when reacting with a reactive metal like magnesium, an acid forms a salt and hydrogen gas rather than carbon dioxide, meaning Statement 4 is incorrect and confirming option C as the correct combination.
✅ Answer: (C)
✅ Answer: (C)
▶️ Answer/Explanation
Universal indicator paper shifting to purple confirms that solution Z is a strong alkali with an elevated pH ($\text{pH} \approx 12\text{–}14$). Under Cambridge IGCSE guidelines, individual indicators display distinct, fixed color profiles across different chemical mediums: methyl orange turns red in acidic solutions but becomes yellow in neutral or alkaline conditions, while thymolphthalein remains completely colourless in acidic or neutral environments and transitions to a vivid blue in highly alkaline ranges. Consequently, testing an alkaline solution like Z yields yellow with methyl orange and blue with thymolphthalein, selecting row A as the single correct suite of configurations.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
According to standard solubility guidelines, most chloride salts dissolve easily in an aqueous medium, but lead(II) chloride stands out as a clear exception that remains insoluble. In a similar manner, while the majority of sulfate salts are highly soluble, lead(II) sulfate is explicitly classified as an exception that forms an insoluble precipitate. Because both of these specific chemical compounds fail to dissolve significantly in water, they are both correctly designated as insoluble.
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
Oxides are classified as acidic or basic based on their non-metallic or metallic character, respectively. Group 1 consists entirely of metallic oxides (Mg, Fe, Cu), meaning they are all basic oxides. Group 4 consists entirely of non-metallic oxides (N, Br, P), meaning they are all acidic oxides. Groups 2 and 3 contain a mixture of acidic, basic, and amphoteric oxides, which makes option C the only correct statement.
✅ Answer: (C)
✅ Answer: (C)
▶️ Answer/Explanation
To safely synthesize a soluble salt from an acid and an insoluble base, you start by warming the dilute acid to increase the rate of reaction[cite: 517, 1068]. Next, adding the solid metal oxide in excess ensures that every molecule of acid is completely neutralized[cite: 520]. The mixture is then filtered to cleanly separate and remove the unreacted solid oxide residue from the soluble salt filtrate[cite: 517, 938, 939]. Finally, heating the filtrate to evaporate the water to the crystallization point and letting it cool allows pure crystals to systematically form[cite: 968].
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
To determine the most violent reaction, we must identify the most reactive elements from both groups involved. In Group I, the reactivity of alkali metals increases as you move down the group, making potassium significantly more reactive than lithium. Conversely, in Group VII, the reactivity of halogens decreases down the group, meaning chlorine is much more reactive than iodine. Therefore, combining the most reactive alkali metal available (potassium) with the most reactive halogen available (chlorine) will produce the most vigorous and violent chemical reaction. The combination of potassium and chlorine perfectly fits these established periodic trends.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
As an alkali metal located in Group I of the Periodic Table, rubidium shares the characteristic group family features of being a relatively soft metal that can be easily cut with a knife[cite: 549, 550]. Furthermore, because chemical reactivity with water systematically increases moving down Group I [cite: 552], rubidium reacts exceptionally vigorously and explosively with water to release flammable hydrogen gas and produce a highly alkaline hydroxide solution[cite: 496, 601]. This combination of a soft texture and highly reactive nature means that row C perfectly contrasts its properties.
✅ Answer: (C)
✅ Answer: (C)
▶️ Answer/Explanation
The halogens are a group of non-metals in Group VII of the Periodic Table that exhibit distinct physical properties and a trend in their states of matter at room temperature. As we move down the group, the melting and boiling points increase, causing the physical state to change from gas to liquid to solid. Chlorine is a pale yellow-green gas, while iodine is a grey-black solid. Bromine, positioned between them, is uniquely a dense liquid at room temperature and pressure. Furthermore, it possesses a very characteristic, strong red-brown colour, making option A the only correct and complete description of its physical state and appearance.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
In the grid arrangement of the Periodic Table, elements reveal a distinct transition from metallic to non-metallic character as you move across a period from left to right. This structural organization places highly conductive, malleable metallic elements on the far-left and center positions, while non-metals populate the right side. Consequently, an element marked on the left section of a period belongs to the metal category, perfectly distinguishing it from the non-metallic options on the right.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
To identify the correct compound, we must determine the period (horizontal row) for each constituent element using the Periodic Table[cite: 540, 1229]. Lithium nitrate ($\text{LiNO}_3$) is composed of lithium ($\text{Li}$), nitrogen ($\text{N}$), and oxygen ($\text{O}$), all of which possess exactly two occupied electron shells and reside entirely within Period 2[cite: 221, 1229]. The remaining options contain elements spanning different horizontal rows, such as oxygen ($\text{O}$) in Period 2 mixed with Period 3 elements like aluminum ($\text{Al}$), sulfur ($\text{S}$), or sodium ($\text{Na}$)[cite: 1229].
✅ Answer: (C)
✅ Answer: (C)
▶️ Answer/Explanation
Silver is situated near the very bottom of the reactivity series, placing it significantly below hydrogen. Because of this low position, silver is an extremely unreactive metal under standard laboratory conditions. When placed in cold water or exposed to steam, silver lacks the necessary reactivity to displace hydrogen and form a metal oxide or hydroxide, resulting in no observable reaction. Similarly, silver cannot displace hydrogen ions from dilute hydrochloric acid, meaning no hydrogen gas or aqueous salt will be produced. Therefore, all three tests will yield a negative result, as accurately represented by the three crosses in the final row.
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
Inside a blast furnace, carbon dioxide gas rises and reacts with fresh incoming hot coke (carbon), causing the carbon dioxide to lose oxygen and undergo reduction into carbon monoxide gas ($C + CO_2 \rightarrow 2CO$). This makes statement B correct, as carbon monoxide serves as the primary reducing agent for the furnace. The remaining options are false because hematite undergoes reduction rather than oxidation, air is injected to combust coke to provide thermal energy rather than oxidize iron, and slag floats safely on top because it is significantly less dense than molten iron.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
An alloy is formally defined as a physical mixture containing a primary metal combined with one or more other elements[cite: 617]. Because its components are physically mixed rather than chemically combined, it behaves as a mixture rather than a compound, which rules out options A and B[cite: 617]. These added elements can be other metals, such as zinc combined with copper to yield brass, or non-metals, like carbon blended with iron to manufacture steel[cite: 618, 619], meaning option C is the correct answer.
✅ Answer: (C)
✅ Answer: (C)
▶️ Answer/Explanation
In tube S, the unpainted iron nail reacts freely with the trapped oxygen gas and water vapor, actively consuming oxygen as it corrodes into hydrated iron(III) oxide[cite: 642]. This active uptake of gaseous oxygen reduces the internal air pressure inside tube S, causing atmospheric pressure to push the water level upward[cite: 1119]. Conversely, in tube T, the protective layer of paint acts as a barrier that blocks oxygen and moisture from contacting the metal [cite: 642], successfully preventing corrosion and leaving the air volume and water level unchanged[cite: 1119].
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
Clean, dry air is a physical mixture of different gases that are not chemically bonded together, meaning options A and D are incorrect because they label it a compound. According to the syllabus, air is composed of approximately 78% nitrogen and 21% oxygen, meaning the proportions given in option B are reversed. Therefore, option C is the only completely accurate description because it properly identifies air as a mixture containing multiple gaseous components including nitrogen and oxygen.
✅ Answer: (C)
✅ Answer: (C)
▶️ Answer/Explanation
Photosynthesis is an endothermic chemical process where green plants trap light energy using chlorophyll to fuel a reaction between carbon dioxide and water. This metabolic path converts inorganic raw materials specifically into organic chemical storage as glucose, releasing gaseous oxygen back into the atmosphere as a vital byproduct. Consequently, the literal word representation for this synthesis is written out as carbon dioxide + water → glucose + oxygen, matching row A perfectly.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
According to the Cambridge IGCSE Chemistry syllabus, oxides of nitrogen are specifically identified as air pollutants that lead to acid rain, photochemical smog, and respiratory problems. Other listed pollutants only cause a subset of these issues; for example, carbon monoxide is primarily a toxic gas, methane is associated with global warming, and particulates lead to respiratory problems and cancer but not smog or acid rain. Therefore, oxides of nitrogen are the unique pollutant responsible for all three specified environmental and health hazards.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
Petroleum is naturally defined as a complex mixture of different hydrocarbons with varying chain lengths. To isolate these chemical groups into distinct, smaller portions called fractions, the physical process of fractional distillation is utilized. Cracking, on the other hand, is a subsequent chemical breakdown process used to convert large alkanes into smaller alkanes and alkenes rather than separating the raw oil. Therefore, option D accurately characterizes petroleum as a mixture and its key industrial separation method as fractional distillation.
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
A homologous series is defined as a family of organic compounds that share the same functional group and general formula, which gives them highly similar chemical properties. Successive members of a series differ from one another by a structural $-CH_2-$ unit, meaning that they have progressively increasing relative molecular masses rather than identical ones. Ethane and propane are both saturated hydrocarbons belonging to the alkane family, whereas ethene contains a double bond and belongs to the alkene family. Therefore, statements 1 and 4 are correct, while statements 2 and 3 are incorrect.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
Compound P contains the $-\text{OH}$ functional group bound to an aliphatic carbon chain, which directly defines its chemical family as an alcohol[cite: 758, 760]. Compound Q features a distinct carbon-carbon covalent double bond ($\text{C}=\text{C}$), which establishes its identity as an unsaturated alkene homologous series member[cite: 757, 772]. Consequently, row B is the only selection that accurately identifies the structural classifications for both organic compounds[cite: 757, 758].
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
Ethanol is widely manufactured through the biological fermentation of aqueous glucose solutions using enzymes in yeast, and it is a key substance utilized as a renewable fuel source. In contrast, diesel and kerosene are fossil fuel fractions isolated directly from petroleum via physical fractional distillation in a fractionating column rather than biological pathways. Hydrogen can be produced via alternative industrial methods, such as the chemical cracking of large alkane molecules alongside alkenes. Therefore, option B is the only substance appropriately matched to its method of preparation.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
Plastics are non-biodegradable synthetic polymers that persist in the environment for hundreds of years instead of decomposing quickly. When plastics find their way into water systems, they accumulate heavily in marine environments where they pose severe entanglement and ingestion hazards to aquatic organisms. Incineration of plastic waste is also an environmental challenge because it releases highly toxic and hazardous gases rather than safe products. Finally, because plastics are completely insoluble in water, they cannot be disposed of by being dissolved and pumped away.
✅ Answer: (C)
✅ Answer: (C)
▶️ Answer/Explanation
In paper chromatography, components within a mixture are separated based on their solubility as they travel up the paper. To identify which specific substances are present in an unknown sample, the height of its separated spots is compared horizontally with the spots of pure reference materials. In this chromatogram, the two spots produced by substance X align perfectly at the exact same heights as the individual spots for dye 2 and dye 3. This horizontal match confirms that substance X is composed exclusively of those two components, making option C the correct answer.
✅ Answer: (C)
✅ Answer: (C)
▶️ Answer/Explanation
The yellow flame test confirms the presence of sodium ions ($\text{Na}^+$), as potassium ions produce a characteristic lilac flame. When substance G is warmed with aqueous sodium hydroxide and aluminium foil, the generation of an alkaline gas (ammonia) that turns damp red litmus blue specifically identifies the presence of the nitrate anion ($\text{NO}_3^-$). Combining these qualitative results concludes that substance G must be sodium nitrate. Therefore, chloride options (A and C) and potassium options (A and B) are completely ruled out.
✅ Answer: (D)
✅ Answer: (D)