JEE Main 2022 · 27 July · evening · Numerical answer · +4 / −0
Among the following ores Bauxite, Siderite, Cuprite, Calamine, Haematite, Kaolinite, Malachite, Magnetite, Sphalerite, Limonite, Cryolite, the number of principal ores if iron is _____________.
Answer and solution
Answer 4
Solution
Chemistry ma’am · 3 steps
Write the formula next to each ore name, then count only the ones whose metal is Fe.
- Match ore to metal. An ore name alone tells you little. Its formula shows which metal it is mined for, so sort the eleven names by metal.
Metal Ores in the list Formulae Aluminium Bauxite, Kaolinite, Cryolite Al₂O₃.xH₂O, Al₂(OH)₄Si₂O₅, Na₃AlF₆ Iron Siderite, Haematite, Magnetite, Limonite FeCO₃, Fe₂O₃, Fe₃O₄, Fe₂O₃.3H₂O Copper Cuprite, Malachite Cu₂O, CuCO₃.Cu(OH)₂ Zinc Calamine, Sphalerite ZnCO₃, ZnS - Iron ores. Siderite is the carbonate, Haematite and Magnetite are oxides, and Limonite is the hydrated oxide. All four are principal ores of iron.
- So. The number of iron ores in the list is 4.
The common slip: 3. Missing Limonite, because its name does not hint at iron, gives 3. It is hydrated ferric oxide, Fe₂O₃.3H₂O.
The idea to keep. For iron, remember the four: Haematite Fe₂O₃, Magnetite Fe₃O₄, Limonite Fe₂O₃.3H₂O and Siderite FeCO₃. Iron pyrites FeS₂ is a mineral, not a source of iron.
Answer from the NTA final answer key. Solution by PrepWiser.