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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In benzene, all six carbon–carbon bond lengths are equal (about 139 pm) because of:
सही उत्तर: ग) resonance (delocalisation of π electrons)
The π electrons are delocalised over the ring, so each C–C bond is intermediate between a single (154 pm) and a double (134 pm) bond.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Formation of an ionic bond between two atoms is favoured when:
सही उत्तर: ख) the metal has low ionisation energy and the non-metal has a high (more negative) electron gain enthalpy
Ionic bonding needs easy electron loss by the metal, easy electron gain by the non-metal, and a high lattice energy.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The correct decreasing order of bond angles is:
सही उत्तर: क) CH₄ > NH₃ > H₂O
With 0, 1 and 2 lone pairs respectively, the angles are about 109.5°, 107° and 104.5°, since lone pair repulsion compresses the bond angle.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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o-Nitrophenol has a lower boiling point than p-nitrophenol because:
सही उत्तर: घ) o-nitrophenol shows intramolecular hydrogen bonding while p-nitrophenol shows intermolecular hydrogen bonding
Intramolecular H-bonding in the ortho isomer prevents association of molecules, whereas the para isomer associates through intermolecular H-bonds, raising its boiling point.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The geometry of the ammonium ion (NH₄⁺) is:
सही उत्तर: ग) tetrahedral
In NH₄⁺ nitrogen has four bond pairs and no lone pair (sp³), so the ion is tetrahedral with H–N–H angles of 109.5°.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The hybridisation of phosphorus and the shape of the PCl₅ molecule (gaseous) are:
सही उत्तर: ख) sp³d, trigonal bipyramidal
P has five bond pairs and no lone pair, giving sp³d hybridisation and a trigonal bipyramidal shape.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The shape of the SF₄ molecule is:
सही उत्तर: क) see-saw
S has four bond pairs and one lone pair (sp³d); the lone pair occupies an equatorial position, giving a see-saw shape.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The hybridisation of carbon in carbon dioxide (CO₂) is:
सही उत्तर: घ) sp
Carbon forms two σ bonds and two π bonds with no lone pairs; two hybrid orbitals are needed, so it is sp-hybridised and the molecule is linear.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The second ionisation energy of sodium is very much larger than its first because:
सही उत्तर: ग) the second electron must be removed from a stable noble-gas (neon) core
After losing its 3s electron, Na⁺ has the stable [Ne] configuration; removing a 2p electron from this compact core needs far more energy.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The correct order of radii of iron and its ions is:
सही उत्तर: ख) Fe > Fe²⁺ > Fe³⁺
Removing electrons increases the effective nuclear charge per electron, so the more positive the ion, the smaller it is.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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