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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The number of atoms present in 0.1 mol of ozone (O₃) is about (N_A = 6.022 × 10²³):
सही उत्तर: घ) 1.81 × 10²³
0.1 mol O₃ has 0.1 N_A molecules, each with 3 atoms: 0.3 × 6.022 × 10²³ ≈ 1.81 × 10²³ atoms.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Chromatography separates the components of a mixture on the basis of their:
सही उत्तर: घ) different adsorption or partition between a stationary and a mobile phase
Components distribute differently between the stationary phase and the moving phase, so they travel at different rates and separate.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Aniline, which is immiscible with water and volatile in steam, is purified by:
सही उत्तर: ग) steam distillation
Steam distillation suits water-immiscible liquids that are steam-volatile; the mixture boils below 100 °C, avoiding decomposition.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Starch is a polymer of:
सही उत्तर: ख) α-D-glucose
Starch (amylose and amylopectin) consists of α-D-glucose units joined by glycosidic linkages; cellulose is made of β-D-glucose.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Bakelite is a thermosetting polymer obtained from:
सही उत्तर: क) phenol and formaldehyde
Bakelite is formed by condensation polymerisation of phenol with formaldehyde, forming a cross-linked network.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Gabriel phthalimide synthesis is used to prepare:
सही उत्तर: घ) pure primary aliphatic amines
Potassium phthalimide is alkylated and then hydrolysed to give only primary amines; aryl halides do not react, so aniline cannot be made this way.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The reduction of an acid chloride to an aldehyde with H₂ over palladium on barium sulphate is called the:
सही उत्तर: ग) Rosenmund reduction
In the Rosenmund reduction, BaSO₄ (often with sulphur or quinoline) poisons the Pd catalyst so the aldehyde is not reduced further.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Addition of HCN to an aldehyde or ketone gives a:
सही उत्तर: ख) cyanohydrin
CN⁻ adds to the carbonyl carbon (nucleophilic addition) and the oxygen is protonated, forming a cyanohydrin R₂C(OH)CN.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Diethyl ether heated with excess hydroiodic acid gives:
सही उत्तर: क) ethyl iodide
HI cleaves the C–O bonds; with excess HI the ethanol first formed is also converted, giving two molecules of C₂H₅I.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Phenol reacts with bromine water to give a white precipitate of:
सही उत्तर: घ) 2,4,6-tribromophenol
The strongly activating –OH group allows substitution at both ortho and the para positions in aqueous medium, giving 2,4,6-tribromophenol.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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