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Only gases can be easily compressed because their particles are very far apart with large spaces between them. In solids and liquids, the particles are already packed closely together, so there is very little room to move them closer together. Since water exists as a gas only when it is steam, steam is the only state where water can be compressed to half its original volume.
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At \(25^{\circ}C\), sulfur is well below its melting point of \(113^{\circ}C\), so it is in the solid state. In solids, the particles are held tightly together in a regular, fixed arrangement. They cannot move around, but they do have some energy and vibrate or shake about these fixed positions, which is exactly what Row A describes.
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The brown solid conducting electricity is a classic property of a metal. Since a blue solution also forms, it means part of the solid dissolved while the metal part did not. A pure compound or a pure metal would not separate into two distinct parts like this. The only explanation is that Y is a mixture, containing a soluble blue salt and an insoluble brown metal.
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In an atom, protons have a relative mass of 1 and a positive charge, electrons have a very small relative mass (about 1/1836) and a negative charge, while neutrons have a relative mass of 1 and are neutral, meaning they have no charge. Option A is wrong because electrons have a tiny mass. Option B is wrong for the same reason. Option C is wrong because protons have a positive, not negative, charge. This makes D the only correct statement.
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The electronic configuration shown is 2,8,8, which is a total of 18 electrons. A neutral atom of Argon (Ar) has 18 protons and 18 electrons, so student 1 is correct. A neutral chlorine (Cl) atom has 17 electrons, so student 2 is wrong. A calcium ion \(Ca^{2+}\) has lost 2 electrons, so it has 20 protons but only 18 electrons, giving it the 2,8,8 configuration. Student 3 is also correct.
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Detailed solution:
The definition of an isotope is directly stated in the syllabus: they are atoms of the same element, so they have the same number of protons (atomic number), but they have different numbers of neutrons, giving them different mass numbers. A homologous series relates to organic chemistry, mass number is the total of protons and neutrons, and group number relates to the Periodic Table. Therefore, isotopes perfectly match the given description.
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Detailed solution:
Atom Q with an electronic configuration of 2,8,1 is in Group I and will lose one electron to form a cation with a 1+ charge. Atom R with a configuration of 2,7 is in Group VII and will gain one electron to form an anion with a 1- charge. For the compound to be neutral, one Q⁺ ion must bond with one R⁻ ion, giving the simplest formula RQ.
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Simple molecular compounds consist of small molecules with weak intermolecular forces between them, which means they have low melting and boiling points. They do not conduct electricity because there are no free ions or delocalised electrons. High melting points and malleability are properties of metals or giant covalent structures, not simple molecules. So, from the list, only low boiling point (3) is a typical property of simple molecules.
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In diamond, each carbon atom forms four very strong covalent bonds with other carbon atoms, creating a rigid, tetrahedral network throughout the entire structure. This explains its extreme hardness. Since all the outer shell electrons are locked in these bonds and there are no delocalised electrons or ions, it cannot conduct electricity. Option D perfectly captures both of these structural reasons.
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Complete combustion of a hydrocarbon produces only carbon dioxide and water. By balancing the equation for \(C_4H_{10}\): you need 4 carbon atoms in \(CO_2\) and 10 hydrogen atoms in \(H_2O\). To balance the 2 butane molecules, you have 8 carbons and 20 hydrogens on the left. This requires 8 \(CO_2\) molecules and 10 \(H_2O\) molecules, which means you need 13 \(O_2\) molecules on the left. Equation C is the only one that is correctly balanced and shows complete combustion.
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To calculate the relative formula mass, we add the relative atomic masses (from the Periodic Table): Ca = 40, S = 32, and O = 16. Since there are four oxygen atoms, their total mass is 4 × 16 = 64. Adding these gives: 40 (for Ca) + 32 (for S) + 64 (for O_4) = 136. So, the \(M_r\) of \(CaSO_4\) is 136.
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Molten silver iodide contains Ag⁺ and I⁻ ions. During electrolysis, the positive Ag⁺ ions move to the negative cathode and gain electrons to form solid silver metal. The negative I⁻ ions move to the positive anode and lose electrons to form iodine. Since the electrodes are inert and the compound is molten, no other products like hydrogen or oxygen are possible. This gives silver at the cathode and iodine at the anode.
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Electrolysis of dilute sulfuric acid breaks down water into hydrogen and oxygen gases. Hydrogen gas forms at the cathode and oxygen gas forms at the anode, both of which are colourless. The key is the volume ratio: water (\(H_2O\)) decomposes to give twice the volume of hydrogen as oxygen (2H₂:1O₂). So, for every 10 cm³ of oxygen produced at the anode, 20 cm³ of hydrogen is produced at the cathode.
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An exothermic reaction gives out heat, causing the temperature of the surroundings to rise. To find the most exothermic reaction, we look for the greatest temperature increase. Experiment A shows a decrease of 15°C, C shows a decrease of 13°C (both are endothermic). Experiment D shows an increase of 9°C. Experiment B shows the largest temperature increase, from 20°C to 32°C, which is a rise of 12°C, making it the most exothermic.
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A physical change involves a change in state or appearance without forming a new substance. In the diagram, test-tube A shows ice melting into water. This is just a change of state from solid to liquid (still H₂O), so it is a physical change. The other diagrams likely show reactions where gases are produced, a solid dissolving in acid, or burning, which are all examples of chemical changes where new substances are created.
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To measure the effect of temperature on reaction rate, you absolutely must measure temperature (to see what temperature you’re testing) and time (to see how fast the reaction happens). So, a stop-watch and a thermometer are essential. A balance is for mass, and a gas syringe is for collecting a gas—neither is needed for *any* reaction, as you could be measuring colour change or mass loss instead. For this specific aim, time and temperature are the only must-haves.
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The reaction can go forwards (pink to blue) when heated and backwards (blue to pink) when water is added, which is the definition of a reversible reaction. The pink starting material contains water, making it the hydrated form. When it turns blue, it becomes anhydrous. Since adding water brings the pink colour back, the pink cobalt(II) chloride must be the hydrated version.
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The name iron(III) oxide tells us directly that iron has an oxidation number of +3. We can also calculate it: oxygen always has an oxidation number of -2 in compounds. In \(Fe_2O_3\), the three oxygen atoms give a total negative charge of -6. For the compound to be neutral, the two iron atoms must balance this with a total of +6, meaning each iron atom has a charge of +3.
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Acids react with bases (like copper(II) oxide and copper(II) hydroxide) and with carbonates (like copper(II) carbonate) to form a salt and water (plus carbon dioxide for carbonates). All three of these reactions will produce aqueous copper(II) chloride. However, copper metal itself does not react with dilute hydrochloric acid because copper is below hydrogen in the reactivity series and is not reactive enough to displace hydrogen from the acid.
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In solution X, thymolphthalein is colourless (acidic/neutral) and methyl orange is red (acidic). So, solution X must be an acid. When excess Y is added, thymolphthalein turns blue and methyl orange turns yellow, which are their colours in alkaline conditions. This means Y must be an alkali. Only sodium hydroxide, \(NaOH(aq)\), is an alkali. Hydrochloric acid would keep the solution acidic, and water or salt solution would be neutral, not turning thymolphthalein blue.
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Adding water and filtering separates a soluble solid from an insoluble one. Silver chloride is an insoluble salt, so it will not dissolve in water and will be caught by the filter paper. Ammonium chloride, like most ammonium salts, is soluble in water and will dissolve, passing through the filter paper as the filtrate. In the other options, the mixtures consist of two soluble or two insoluble substances, so simple filtration wouldn’t separate them.
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The Periodic Table has metals on the left side and non-metals on the right. Metals tend to lose electrons to form positive ions (cations), while non-metals tend to gain electrons to form negative ions (anions). So, the left side has metallic elements that form positive ions, and the right side has non-metallic elements that form negative ions. This makes Row A the correct description of this trend.
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As you go down Group I from lithium to sodium to potassium, the atoms get larger and heavier. This causes the density to generally increase. The melting points actually decrease down the group, and the reactivity increases down the group. The total number of electrons increases down a group because the atoms get larger. Therefore, the only correct trend listed is that the density increases.
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At room temperature, chlorine is actually a pale yellow-green gas, not colourless. Bromine is a red-brown liquid, not chlorine. Iodine does exist as a purple gas when it sublimes upon heating, but at room temperature and pressure, it is a grey-black solid. This makes the statement that iodine is a grey-black solid the only accurate description of a halogen’s appearance at r.t.p.
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Transition elements like osmium have typical metallic properties but are distinct from Group I metals. They are known for being very dense, having very high melting points, and critically, they often form coloured compounds. For example, copper(II) sulfate is blue and iron(III) oxide is red-brown. While Group I compounds are typically white, transition element compounds are frequently coloured, making Row A the correct choice.
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Neon is a noble gas found in Group VIII (Group 0/18), not Group VII. Because it has a full outer shell of electrons, it is extremely unreactive and does not react readily with oxygen. Noble gases are also monatomic, meaning they exist as single atoms, unlike diatomic molecules such as \(O_2\) or \(N_2\). The reason for this unreactivity is its stable, full outer electron shell, making D the correct statement.
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A substance that reacts with dilute acids to produce hydrogen gas is a metal. The fact that it forms a basic oxide with both steam and oxygen confirms it’s a metal. Silver is too unreactive to react with dilute acids, so it cannot be the answer. Phosphorus and silicon are non-metals and would form acidic oxides. Magnesium fits all the criteria: it reacts with acids, and its oxide (MgO) is a basic oxide.
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Aluminium is used for overhead power cables precisely because it has a low density (making the cables lighter and easier to support) and because it is a good conductor of electricity. Option A is wrong because aluminium has a low density, not high. Copper is used for wiring because it has excellent ductility, so C is wrong. Copper also has a high density, not low, so D’s description for aircraft manufacture is also incorrect.
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Barrier methods prevent rusting by physically stopping oxygen and water from reaching the iron surface. Coating with plastic (2), greasing (3), and painting (4) all create a physical barrier. Alloying (1), such as making stainless steel, is different—it changes the chemical composition of the iron itself so it doesn’t rust, rather than just providing a physical barrier. Therefore, 2, 3, and 4 are the true barrier methods.
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Thermal decomposition is the breakdown of a compound into simpler substances using heat. In the blast furnace, calcium carbonate (limestone) breaks down when heated to form calcium oxide and carbon dioxide: \(CaCO_3 \rightarrow CaO + CO_2\). Reaction B is combustion, C is a reduction, and D is a redox/reduction reaction. Only reaction A involves a single compound breaking down into two simpler substances upon heating.
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The primary gases in clean, dry air are approximately 78% nitrogen and 21% oxygen. The remaining 1% is mostly noble gases like argon, with a very small amount of carbon dioxide. Carbon monoxide is a toxic pollutant and is not a natural component of clean air. So, the correct row must list 78% nitrogen, 21% oxygen, and then carbon dioxide (not carbon monoxide) as part of the remaining gases.
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Microbes, such as bacteria and viruses that cause diseases like cholera and typhoid, are typically introduced to natural water sources through sewage. Metal compounds can be toxic, and nitrates and phosphates cause environmental problems like deoxygenation of water. However, these are chemical pollutants, not biological ones. Sewage is the specific pollutant that is rich in disease-causing microbes.
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Gas X, a waste gas from animal digestion, is methane (\(CH_4\)). When a hydrocarbon like methane burns, complete combustion with excess oxygen produces carbon dioxide (\(Z\)). Incomplete combustion, which happens when there is insufficient oxygen, produces the toxic gas carbon monoxide (\(Y\)). The correct sequence is therefore Methane \(\rightarrow\) Carbon monoxide \(\rightarrow\) Carbon dioxide, matching row D perfectly.
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Photosynthesis uses light energy and chlorophyll to convert carbon dioxide and water into glucose and oxygen. It actually increases oxygen levels, so A is wrong. It produces oxygen, not a greenhouse gas, so C is wrong. Photosynthesis happens best at moderate temperatures, usually well below \(50^{\circ}C\), so D is wrong. The central reaction is indeed between carbon dioxide and water, making B the only correct description.
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Homologous series L decolourises aqueous bromine, which is the classic test for alkenes (unsaturated compounds). Alkenes have the general formula \(C_nH_{2n}\). Series M dissolves in water to form acidic solutions (pH below 7), which means they are carboxylic acids. The general formula for a carboxylic acid is \(C_nH_{2n+1}COOH\). This pairing of alkene and carboxylic acid general formulas matches Row A exactly.
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An unsaturated hydrocarbon contains at least one carbon-carbon double bond (C=C). By looking at the diagrams, we need to find a molecule that has only carbon and hydrogen atoms and also contains a double bond. The correct structure is ethene (or a similar alkene), which has the formula \(C_2H_4\) and the characteristic C=C double bond that marks it as unsaturated.
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Petroleum is a mixture of hydrocarbons. By definition, a hydrocarbon is a compound containing only the elements hydrogen and carbon. This means every compound in petroleum must contain carbon and hydrogen. Oxygen is not a component of hydrocarbons and is only present if the compound belongs to a different chemical family, like alcohols or acids. So, the correct set is carbon and hydrogen only.
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The primary purpose of any fuel is to release energy, usually in the form of heat and light, when it is burned. This energy is harnessed for various applications. While it’s true that ethanol forms carbon dioxide when burned (\(C_2H_5OH + 3O_2 \rightarrow 2CO_2 + 3H_2O\)), this is a consequence, not the reason it is useful as a fuel. The key reason is the exothermic nature of its combustion, releasing energy.
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The first test with acidified silver nitrate gives a white precipitate. This tells us the anion is a chloride ion (\(Cl^-\)), because silver chloride is white (bromide would give a cream precipitate, and iodide a yellow one). The second test with aqueous sodium hydroxide gives a green precipitate that dissolves in excess NaOH. A green precipitate points to either chromium(III) or iron(II). Crucially, chromium(III) hydroxide dissolves in excess sodium hydroxide, whereas iron(II) hydroxide is insoluble in excess. So the cation must be chromium(III). Therefore, the solid is chromium(III) chloride.
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In paper chromatography, a substance is identified by comparing the distance its spot travels up the paper relative to known reference spots. Two spots are the same substance if they travel the same distance from the baseline. Looking at the chromatogram, mixture W has separated into three distinct spots. By drawing horizontal lines across from these spots, we can see they line up perfectly with reference dyes P, R, and S. No spot in mixture W aligns with dye Q. Therefore, the chromatogram proves that W contains P, R, and S, making option D the correct interpretation.