रसायन विज्ञान – Chemistry MCQ
रसायन विज्ञान – IT प्रवेश
Chemistry · IT Entrance – B.Sc. CSIT, BIT & BCA · ६४१ प्रश्न
६४१ प्रश्न उपलब्ध। मोड छान्नुहोस्:
रसायन विज्ञान: 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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Nylon-6,6 is made from:
सही उत्तर: क) Hexamethylenediamine and adipic acid
Nylon-6,6 is a condensation polymer of hexamethylenediamine and adipic acid, both with six carbons. Caprolactam gives nylon-6, and ethylene glycol + terephthalic acid gives terylene (PET).
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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In the alcoholic fermentation of glucose by yeast, the enzyme zymase converts glucose into:
सही उत्तर: ग) Ethanol and carbon dioxide
C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂, catalysed by zymase. Lactic acid is the product of fermentation in muscles and in milk souring.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Saponification is the:
सही उत्तर: क) Alkaline hydrolysis of fats or oils to form soap
Heating a fat (a triglyceride ester) with NaOH gives glycerol and the sodium salts of fatty acids, which are soap. Esterification is the reverse type of reaction, forming an ester from an acid and an alcohol.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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A silver mirror formed with Tollens' reagent indicates the presence of:
सही उत्तर: घ) An aldehyde
Aldehydes reduce ammoniacal silver nitrate to metallic silver, which forms a mirror on the glass. Simple ketones do not give this test, which is how the two are distinguished.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The Lucas test is used to distinguish between:
सही उत्तर: घ) Primary, secondary and tertiary alcohols
The Lucas reagent (conc. HCl + anhydrous ZnCl₂) gives turbidity immediately with tertiary alcohols, in a few minutes with secondary alcohols, and not at room temperature with primary ones. Amines are distinguished by the Hinsberg test.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Which of the following gives a positive iodoform test?
सही उत्तर: घ) Ethanol
Ethanol is oxidized to ethanal (which has CH₃CO–), so it forms yellow CHI₃ with I₂ and NaOH. Methanol does not have a CH₃CH(OH)– group and gives a negative test.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The reaction of an alkyl halide with sodium metal in dry ether to form a higher alkane is called:
सही उत्तर: क) Wurtz reaction
In the Wurtz reaction, 2R–X + 2Na → R–R + 2NaX, which doubles the carbon chain. The Wurtz–Fittig reaction is the related version that uses an aryl halide.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The peroxide (Kharasch) effect, which gives anti-Markovnikov addition, is observed with:
सही उत्तर: क) HBr only
Only HBr shows the peroxide effect, because its free-radical chain steps are energetically favourable. For HCl and HI one of the radical steps is unfavourable.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Addition of HBr to propene (with no peroxide) mainly gives:
सही उत्तर: क) 2-Bromopropane
By Markovnikov's rule, H adds to the carbon that already has more H atoms, and Br goes to the middle carbon through the more stable secondary carbocation. 1-Bromopropane is the major product only when a peroxide is present.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The number of π electrons in a benzene molecule is:
सही उत्तर: ग) 6
Benzene has three C=C π bonds with two electrons each, giving 6 delocalized π electrons, which satisfies Hückel's (4n + 2) rule for n = 1. 3 is the number of π bonds, not electrons.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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