e":"text","order":4,"title":"Analyze the remaining Option B","content":"Now we evaluate the final statement regarding ionic radii:\n\n* Both $\\text{S}^{2-}$ and $\\text{Cl}^-$ are **isoelectronic** species, meaning they share the same electron configuration: $1\text{s}^2 2\text{s}^2 2\text{p}^6 3\text{s}^2 3\text{p}^6$ (18 electrons).\n* Sulfur has $16$ protons in its nucleus, while chlorine has $17$ protons.\n* Because chlorine has more protons, its nucleus exerts a stronger electrostatic pull on the same $18$ electrons, drawing them closer and making the ionic radius of $\\text{Cl}^-$ **smaller** than that of $\\text{S}^{2-}$.\n\nTherefore, the statement that $\\text{Cl}^-$ has a larger ionic radius than $\\text{S}^{2-}$ is **incorrect**."},{"type":"text","order":5,"title":"Confirm the correct answer","content":"By systematically eliminating the correct statements, we find that the only false statement is Option B.","highlights":[{"text":"correct answer","index":1,"location":"option"}]}]}],"generatedAt":"2026-06-11T09:04:51.130Z","modelVersion":"gemini-3.5-flash","explanationVersion":"v2"},"firstAttemptFullMarks":null},{"id":"4f30f906-5778-4654-9232-da372680fcd0","revisionId":"1a655c35-2401-4154-a2ae-fb09900f5f7a","questionNumber":null,"questionType":"LA","specification":"","difficulty":6,"difficultyBand":"medium","totalMarks":7,"sourceTitle":null,"calculatorUse":null,"parts":[{"id":"9a7a1cc2-20b2-4fa2-b085-773d4e03511f","label":"a","content":"$3f","markscheme":"- Calculates the amount of thiosulfate ions: $n(\\text{S}_2\\text{O}_3^{2-}) = \\frac{24.60}{1000} \\times 0.0500 = 0.00123\\text{ mol}$ M1\n- Calculates the amount of iodine: $n(\\text{I}_2) = \\frac{0.00123}{2} = 0.000615\\text{ mol}$ M1\n- Scales up to find $n(\\text{ClO}^-)$ in the original sample: $n(\\text{ClO}^-) = 0.000615 \\times \\frac{250}{25.0} = 0.00615\\text{ mol}$ M1\n- Calculates the mass of $\\text{NaClO}$ using molar mass $74.5\\text{ g mol}^{-1}$: $\\text{mass} = 0.00615 \\times 74.5 = 0.458175\\text{ g}$ M1\n- Calculates the mass of the original disinfectant sample: $\\text{mass of sample} = 15.0 \\times 1.12 = 16.8\\text{ g}$ M1\n- Evaluates the percentage by mass to 3 significant figures: $\\frac{0.458175}{16.8} \\times 100 = 2.73\\%$ A1","marks":6,"order":0,"markingRubric":null,"explanation":{"methods":[{"id":"mole_based_stoichiometry","label":"Mole-Based Stoichiometry","steps":[{"type":"text","order":0,"title":"Calculate thiosulfate moles","content":"First, we calculate the absolute amount of thiosulfate ions ($\\text{S}_2\\text{O}_3^{2-}$) used in the titration. \n\nWe are given the volume of the titre is $24.60\\text{ cm}^3$ and its concentration is $0.0500\\text{ mol dm}^{-3}$.\n\nUsing the formula:\n$$n = c \\times V$$\n\n$$\\begin{aligned} n(\\text{S}_2\\text{O}_3^{2-}) &= 0.0500\\text{ mol dm}^{-3} \\times \\frac{24.60\\text{ cm}^3}{1000} \\\\ &= 1.23 \\times 10^{-3}\\text{ mol} \\quad \\text{(or } 0.00123\\text{ mol)} \\end{aligned}$$"},{"type":"text","order":1,"title":"Determine iodine moles","content":"Next, we relate the moles of thiosulfate to the moles of iodine ($\\text{I}_2$) produced in the reaction.\n\nFrom the second chemical equation:\n$$2\\text{S}_2\\text{O}_3^{2-}\\text{(aq)} + \\text{I}_2\\text{(aq)} \\rightarrow 2\\text{I}^-\\text{(aq)} + \\text{S}_4\\text{O}_6^{2-}\\text{(aq)}$$\n\nThe stoichiometry between $\\text{S}_2\\text{O}_3^{2-}$ and $\\text{I}_2$ is $2 : 1$.\n\n$$\\begin{aligned} n(\\text{I}_2) &= \\frac{1}{2} \\times n(\\text{S}_2\\text{O}_3^{2-}) \\\\ &= \\frac{1.23 \\times 10^{-3}\\text{ mol}}{2} \\\\ &= 6.15 \\times 10^{-4}\\text{ mol} \\quad \\text{(or } 0.000615\\text{ mol)} \\end{aligned}$$"},{"type":"text","order":2,"title":"Determine chlorate(I) moles","content":"Now we connect the moles of iodine back to the amount of chlorate(I) ions ($\\text{ClO}^-$) present in the $25.0\\text{ cm}^3$ aliquot.\n\nFrom the first chemical equation:\n$$\\text{ClO}^-\\text{(aq)} + 2\\text{H}^+\text{(aq)} + 2\\text{I}^-\\text{(

Group 7(17), the halogens

Question 4

Group 7(17), the halogens Questions

Group 7(17), the halogens

Question 4

Group 7(17), the halogens Questions