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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Oxidation of a secondary alcohol with acidified potassium dichromate gives:
सही उत्तर: ग) a ketone
R₂CHOH loses two hydrogens to give R₂C=O, a ketone; primary alcohols give aldehydes and then acids.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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An alkyl chloride is converted to an alkyl iodide by heating with sodium iodide in dry acetone. This is the:
सही उत्तर: ख) Finkelstein reaction
The Finkelstein reaction is driven forward because the NaCl formed is insoluble in acetone and precipitates.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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In electrophilic substitution, the chlorine atom of chlorobenzene is:
सही उत्तर: क) deactivating but ortho/para-directing
Its −I effect withdraws electron density (deactivating), but its +R effect donates electrons to the ortho and para positions, so it directs o/p.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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In the nitration of benzene with a mixture of concentrated HNO₃ and H₂SO₄, the attacking electrophile is:
सही उत्तर: घ) NO₂⁺
H₂SO₄ protonates HNO₃, which loses water to form the nitronium ion NO₂⁺, the electrophile.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Dehydrobromination of 2-bromobutane with alcoholic KOH gives mainly:
सही उत्तर: ग) but-2-ene
By Saytzeff's rule, the more substituted (more stable) alkene, but-2-ene, is the major product.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Heating an alkyl halide with alcoholic potassium hydroxide mainly gives:
सही उत्तर: ख) an alkene
Alcoholic KOH removes HX (dehydrohalogenation, β-elimination), forming an alkene; aqueous KOH gives an alcohol.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The number of chiral (asymmetric) carbon atoms in the open-chain form of glucose is:
सही उत्तर: क) 4
C-2, C-3, C-4 and C-5 each carry four different groups; C-1 (CHO) and C-6 (CH₂OH) are not chiral.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Diethyl ether (C₂H₅OC₂H₅) and methyl propyl ether (CH₃OC₃H₇) are examples of:
सही उत्तर: घ) metamers
Both are ethers of formula C₄H₁₀O differing only in the alkyl groups on either side of the functional group, which is metamerism.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The IUPAC name of CH₃CH₂COOH is:
सही उत्तर: ग) propanoic acid
The longest chain including the –COOH carbon has three carbons, so it is propanoic acid.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The metal present at the centre of the chlorophyll molecule is:
सही उत्तर: ख) magnesium
Chlorophyll is a magnesium–porphyrin complex; haemoglobin contains iron and vitamin B₁₂ contains cobalt.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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