रसायन विज्ञान (Chemistry) – Chemistry MCQ
रसायन विज्ञान (Chemistry) – इन्जिनियरिङ प्रवेश
Chemistry · Engineering Entrance – Mathematics, Physics, Chemistry & English · ७२८ प्रश्न
७२८ 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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Anhydrous AlCl₃ is used as a catalyst in:
सही उत्तर: ग) Friedel–Crafts alkylation
Anhydrous AlCl₃, a Lewis acid, generates the carbocation (or acylium ion) electrophile in Friedel–Crafts reactions. Hydrogenation uses metal catalysts such as Ni, Pt or Pd.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The electrophile in the nitration of benzene with a mixture of conc. HNO₃ and conc. H₂SO₄ is:
सही उत्तर: ख) NO₂⁺
Sulphuric acid protonates nitric acid, which loses water to form the nitronium ion NO₂⁺, the attacking electrophile. NO₃⁻ and NO₂⁻ are anions and cannot act as electrophiles towards the electron-rich ring.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The reaction of an alkyl halide with sodium metal in dry ether to give a higher alkane is called:
सही उत्तर: क) Wurtz reaction
In the Wurtz reaction 2RX + 2Na → R–R + 2NaX in dry ether. The Sandmeyer reaction converts diazonium salts to aryl halides using copper(I) salts.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Addition of HBr to propene in the presence of an organic peroxide gives mainly:
सही उत्तर: घ) 1-Bromopropane
Peroxide causes free-radical addition (Kharasch or peroxide effect), giving the anti-Markovnikov product 1-bromopropane. This effect is seen only with HBr, not HCl or HI.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Addition of HBr to propene in the absence of peroxide gives mainly:
सही उत्तर: ग) 2-Bromopropane
By Markovnikov's rule, H adds to the carbon with more hydrogens and Br to the more substituted carbon, through the more stable secondary carbocation. 1-Bromopropane forms in the presence of peroxide (anti-Markovnikov addition).
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The number of structural isomers possible for pentane (C₅H₁₂) is:
सही उत्तर: ख) 3
C₅H₁₂ has three structural isomers: n-pentane, 2-methylbutane and 2,2-dimethylpropane. Two isomers is the answer for butane (C₄H₁₀).
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The IUPAC name of CH₃COCH₃ is:
सही उत्तर: क) Propanone
CH₃COCH₃ is a three-carbon ketone, so it is propanone (common name acetone). Propanal (CH₃CH₂CHO) is the isomeric aldehyde.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The brown ring test is used to detect the:
सही उत्तर: घ) Nitrate ion
With FeSO₄ and conc. H₂SO₄, nitrate gives a brown ring of [Fe(H₂O)₅NO]²⁺ at the junction of the liquids. Sulphate is tested with BaCl₂ (white precipitate).
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The coordination number of the central metal in [Co(NH₃)₆]³⁺ is:
सही उत्तर: ग) 6
Six monodentate NH₃ ligands are attached to Co, so the coordination number is 6. Three is the oxidation state of cobalt, not the coordination number.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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In the complex ion [Fe(CN)₆]⁴⁻, the oxidation state of iron is:
सही उत्तर: ख) +2
Each CN⁻ is −1, so x + 6(−1) = −4, giving x = +2. The ion [Fe(CN)₆]³⁻ (ferricyanide) has Fe in the +3 state.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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