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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The number of moles in 36 g of water (H₂O = 18 g/mol) is:
सही उत्तर: घ) 2
n = mass/molar mass = 36/18 = 2 mol.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Which of the following is the strongest acid in aqueous solution?
सही उत्तर: ग) HI
Acid strength of the hydrogen halides increases down the group because the H–X bond becomes weaker, so HI is the strongest. HF is a weak acid because of its very strong H–F bond.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The coordination number of Na⁺ in the sodium chloride (rock salt) crystal is:
सही उत्तर: ग) 6
In NaCl, each Na⁺ is surrounded octahedrally by six Cl⁻ ions, and each Cl⁻ by six Na⁺. A coordination number of 8 is found in CsCl.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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According to molecular orbital theory, the bond order of O₂ is:
सही उत्तर: ख) 2
O₂ has 8 bonding and 4 antibonding valence electrons, so bond order = (8 − 4)/2 = 2. It also has two unpaired electrons, which makes it paramagnetic. Bond order 3 is for N₂.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The scattering of light by colloidal particles, which makes the path of a light beam visible, is called:
सही उत्तर: ग) Tyndall effect
Colloidal particles are big enough to scatter light, so the beam is visible (Tyndall effect). Brownian motion is the random zig-zag movement of colloidal particles.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The van't Hoff factor (i) for NaCl, assuming complete dissociation in dilute aqueous solution, is:
सही उत्तर: घ) 2
NaCl → Na⁺ + Cl⁻ gives 2 particles per formula unit, so i = 2. i = 3 would apply to a salt such as CaCl₂ or Na₂SO₄.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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In the nitration of benzene with a mixture of concentrated HNO₃ and H₂SO₄, the electrophile is:
सही उत्तर: क) NO₂⁺
H₂SO₄ protonates HNO₃, which then loses water to form the nitronium ion NO₂⁺, the electrophile that attacks the ring. HSO₄⁻ is only a by-product.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The catalyst used in Friedel–Crafts alkylation of benzene is:
सही उत्तर: ग) Anhydrous AlCl₃
Anhydrous AlCl₃, a Lewis acid, produces the carbocation electrophile from an alkyl halide. Pd/BaSO₄ is the Rosenmund catalyst, used to reduce acid chlorides to aldehydes.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Phenol is more acidic than ethanol because:
सही उत्तर: घ) The phenoxide ion is stabilized by resonance
The negative charge on the phenoxide ion is delocalized over the benzene ring, which stabilizes it and favours ionization. The ethoxide ion has no resonance and is destabilized by the electron-donating ethyl group.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The monomer of PVC is:
सही उत्तर: ख) Vinyl chloride (CH₂=CHCl)
PVC (polyvinyl chloride) is made by addition polymerization of vinyl chloride. Tetrafluoroethylene is the monomer of Teflon.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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