रसायन विज्ञान (Chemistry) – Chemistry MCQ
रसायन विज्ञान (Chemistry) – CEE प्रवेश
Chemistry · Medical Entrance (CEE) – Physics, Chemistry, Biology & MAT · ४१० प्रश्न
४१० प्रश्न उपलब्ध। मोड छान्नुहोस्:
रसायन विज्ञान (Chemistry): प्रश्न र उत्तर
सही लागेको विकल्पमा थिच्नुहोस्। सही भए हरियो, गलत भए रातो देखिन्छ; ३ सेकेन्डपछि सही उत्तर र व्याख्या देखिन्छ।
सही: ० / ०
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The brown ring test is used to detect:
सही उत्तर: घ) Nitrate ion
Nitrate with FeSO₄ and conc. H₂SO₄ forms a brown ring of [Fe(H₂O)₅(NO)]²⁺ at the junction of liquids. Sulphate is usually detected by a white precipitate with BaCl₂.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The chromyl chloride test is used to detect the presence of:
सही उत्तर: ख) Chloride ion
Heating a chloride with K₂Cr₂O₇ and conc. H₂SO₄ gives orange-red CrO₂Cl₂ vapours. Bromides and iodides do not form chromyl compounds, so the test is specific for chloride.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Zirconium and hafnium have almost identical atomic radii because of:
सही उत्तर: घ) Lanthanide contraction
Poor shielding by 4f electrons causes a steady decrease in size across the lanthanides, cancelling the expected increase from period 5 to 6. Hence Zr and Hf are very hard to separate.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Heating a sulphide ore strongly in excess of air to convert it into its oxide is called:
सही उत्तर: ग) Roasting
Roasting heats the ore in air, e.g. 2ZnS + 3O₂ → 2ZnO + 2SO₂. Calcination is heating in limited or no air, usually for carbonate ores.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The froth flotation method is mainly used to concentrate:
सही उत्तर: घ) Sulphide ores
Sulphide ore particles are preferentially wetted by oil and carried up by the froth, while gangue is wetted by water and sinks. Bauxite (an oxide ore) is concentrated by leaching.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The coordination number of cobalt in [Co(NH₃)₆]Cl₃ is:
सही उत्तर: घ) 6
Six NH₃ ligands are directly bonded to Co³⁺ inside the coordination sphere, so its coordination number is 6. The three Cl⁻ ions are outside the sphere as counter-ions.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The oxidation state of iron in K₄[Fe(CN)₆] is:
सही उत्तर: घ) +2
With 4 K⁺ (+4) and 6 CN⁻ (−6), iron must be +2 for neutrality. In K₃[Fe(CN)₆] (potassium ferricyanide), iron is +3.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The spin-only magnetic moment of Cr³⁺ (Z of Cr = 24) is approximately:
सही उत्तर: ख) 3.87 BM
Cr³⁺ is 3d³ with 3 unpaired electrons, so μ = √[n(n+2)] = √15 ≈ 3.87 BM. 5.92 BM corresponds to 5 unpaired electrons (e.g. Mn²⁺).
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The colour of most transition metal ions in aqueous solution is due to:
सही उत्तर: ख) d–d electronic transitions
Partially filled d orbitals split in the presence of ligands, and electrons absorb visible light while jumping between them. Ions with d⁰ or d¹⁰ configurations, like Zn²⁺, are usually colourless.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Depletion of the stratospheric ozone layer is mainly caused by:
सही उत्तर: ग) Chlorofluorocarbons (CFCs)
In the stratosphere, UV light breaks CFCs to release chlorine radicals that destroy ozone catalytically. CO₂ and methane are mainly linked to the greenhouse effect.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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