रसायन विज्ञान (Chemistry) – Chemistry MCQ
रसायन विज्ञान (Chemistry) – CEE प्रवेश
Chemistry · Medical Entrance (CEE) – Physics, Chemistry, Biology & MAT · ४१० प्रश्न
४१० 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 molecules is paramagnetic?
सही उत्तर: ख) O₂
MO theory shows O₂ has two unpaired electrons in degenerate π* orbitals, so it is paramagnetic. N₂, F₂ and CO have all electrons paired.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The bond order of the O₂⁺ ion is:
सही उत्तर: ग) 2.5
Removing one electron from an antibonding π* orbital of O₂ (bond order 2) gives O₂⁺ with bond order (10 − 5)/2 = 2.5. 1.5 is the bond order of O₂⁻.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Which of the following molecules has zero dipole moment?
सही उत्तर: ख) CO₂
CO₂ is linear, so the two equal C=O bond dipoles cancel each other. H₂O is bent, so its bond dipoles do not cancel.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The hybridisation of phosphorus in PCl₅ is:
सही उत्तर: घ) sp³d
Phosphorus uses one s, three p and one d orbital to form five bonds, giving sp³d hybridisation and a trigonal bipyramidal shape. sp³d² corresponds to six bonds, as in SF₆.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The geometry of the SF₆ molecule is:
सही उत्तर: ख) Octahedral
Sulphur in SF₆ is sp³d² hybridised with six bond pairs, giving an octahedral geometry. Trigonal bipyramidal geometry is seen in PCl₅ (sp³d).
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The H–O–H bond angle in a water molecule is approximately:
सही उत्तर: ग) 104.5°
Two lone pairs on oxygen compress the tetrahedral angle down to about 104.5°. 107° is the bond angle in NH₃, which has only one lone pair.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The shape of the ammonia (NH₃) molecule is:
सही उत्तर: ग) Trigonal pyramidal
N in NH₃ is sp³ hybridised with three bond pairs and one lone pair, giving a trigonal pyramidal shape. The electron-pair geometry is tetrahedral, but the molecular shape is not.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The series of lines in the hydrogen spectrum that lies in the visible region is the:
सही उत्तर: ग) Balmer series
Balmer lines arise from transitions ending at n = 2 and fall in the visible region. The Lyman series (ending at n = 1) lies in the ultraviolet.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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According to Bohr's model, the energy of the electron in the second orbit (n = 2) of a hydrogen atom is:
सही उत्तर: ग) −3.4 eV
Eₙ = −13.6/n² eV, so E₂ = −13.6/4 = −3.4 eV. −1.51 eV is the energy for n = 3.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The ground-state electronic configuration of chromium (Z = 24) is:
सही उत्तर: क) [Ar] 3d⁵ 4s¹
Chromium adopts 3d⁵ 4s¹ because a half-filled d subshell has extra stability from exchange energy. Copper shows a similar exception (3d¹⁰ 4s¹).
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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