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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Which of the following compounds is optically active?
सही उत्तर: ग) Butan-2-ol
In butan-2-ol, C-2 bears four different groups (H, OH, CH₃, C₂H₅), so it is chiral. In propan-2-ol, C-2 carries two identical CH₃ groups and is not chiral.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The general formula of a Grignard reagent is:
सही उत्तर: ख) RMgX
Grignard reagents are alkyl/aryl magnesium halides prepared from RX and Mg in dry ether. RLi is an organolithium compound, not a Grignard reagent.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Heating sodium acetate with soda lime (NaOH + CaO) gives:
सही उत्तर: क) Methane
Soda-lime decarboxylation removes CO₂ from CH₃COONa to give CH₄, an alkane with one carbon fewer. Ethane is the product of Kolbe's electrolysis.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Which aldehyde undergoes the Cannizzaro reaction?
सही उत्तर: ग) Benzaldehyde
The Cannizzaro reaction needs an aldehyde with no α-hydrogen, such as benzaldehyde or formaldehyde. Acetaldehyde has α-hydrogens and undergoes aldol condensation instead.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Aniline reacts with NaNO₂ and dilute HCl at 0–5 °C to form:
सही उत्तर: ख) Benzenediazonium chloride
This is diazotisation; low temperature is needed because benzenediazonium chloride decomposes at higher temperature. On warming, it hydrolyses to phenol.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The carbylamine (isocyanide) test is given by:
सही उत्तर: क) Primary amines
Primary amines heated with chloroform and alcoholic KOH give foul-smelling isocyanides (RNC). Secondary and tertiary amines do not give this test.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Treating an acid amide with Br₂ and aqueous NaOH (Hofmann bromamide reaction) gives:
सही उत्तर: घ) A primary amine with one carbon fewer
In the Hofmann bromamide degradation, RCONH₂ → RNH₂, losing the carbonyl carbon as carbonate. Reduction of an amide with LiAlH₄ instead gives an amine with the same number of carbons.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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In the Lucas test, which type of alcohol produces turbidity immediately at room temperature?
सही उत्तर: ख) Tertiary alcohol
Tertiary alcohols react fastest with conc. HCl/ZnCl₂ because they form the most stable carbocation, giving immediate cloudiness. Secondary alcohols take about 5 minutes, and primary alcohols show no turbidity at room temperature.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Which alcohol gives a positive iodoform test?
सही उत्तर: क) Ethanol
Ethanol contains the CH₃CH(OH)– group, which is oxidised to a CH₃CO– group and gives yellow iodoform (CHI₃). Methanol lacks this group and does not give the test.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Which compound gives a silver mirror with Tollens' reagent?
सही उत्तर: घ) Ethanal (acetaldehyde)
Aldehydes reduce ammoniacal silver nitrate to metallic silver, forming a silver mirror. Ketones like acetone generally do not respond to Tollens' test.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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