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 energy of the electron in the first Bohr orbit of a hydrogen atom is:
सही उत्तर: क) −13.6 eV
Eₙ = −13.6/n² eV, so for n = 1, E = −13.6 eV; the negative sign shows the electron is bound. −3.4 eV is the energy of the second orbit.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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In Bohr's model of the hydrogen atom, the radius of the third orbit compared with the first orbit is:
सही उत्तर: घ) 9 times
The Bohr radius is proportional to n², so r₃/r₁ = 3² = 9. Three times would be true only if radius were directly proportional to n.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The number of unpaired electrons in the Fe³⁺ ion (Fe, Z = 26) is:
सही उत्तर: ग) 5
Fe³⁺ has the configuration [Ar] 3d⁵, with all five d electrons unpaired according to Hund's rule. Four unpaired electrons belong to Fe²⁺ (3d⁶).
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The number of orbitals in a subshell with azimuthal quantum number l = 2 is:
सही उत्तर: क) 5
The number of orbitals in a subshell is 2l + 1 = 5 for l = 2 (a d subshell). Three orbitals belong to a p subshell (l = 1).
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The total number of atoms present in 0.5 mol of ammonia (NH₃) is approximately:
सही उत्तर: घ) 1.204 × 10²⁴
Each NH₃ molecule has 4 atoms, so atoms = 0.5 × 4 × 6.022 × 10²³ ≈ 1.204 × 10²⁴. 3.011 × 10²³ is only the number of molecules.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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When 4 g of H₂ reacts completely with 32 g of O₂, the mass of water formed is:
सही उत्तर: ग) 36 g
4 g H₂ = 2 mol and 32 g O₂ = 1 mol, exactly the 2 : 1 ratio of 2H₂ + O₂ → 2H₂O, giving 2 mol (36 g) of water. This also agrees with the law of conservation of mass (4 + 32 = 36 g).
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The normality of a 0.5 M H₂SO₄ solution is:
सही उत्तर: ख) 1.0 N
Normality = molarity × n-factor; for H₂SO₄ the n-factor is 2, so N = 0.5 × 2 = 1.0 N. 0.25 N comes from dividing instead of multiplying.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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4 g of NaOH is dissolved in water to make 500 mL of solution. Its molarity is:
सही उत्तर: क) 0.2 M
Moles of NaOH = 4/40 = 0.1 mol; molarity = 0.1 mol / 0.5 L = 0.2 M. 0.1 M results if the volume is wrongly taken as 1 L.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The equivalent weight of H₂SO₄ when it is completely neutralised by NaOH is:
सही उत्तर: घ) 49
H₂SO₄ is dibasic, so equivalent weight = molar mass/basicity = 98/2 = 49. 98 would be the equivalent weight only if it acted as a monobasic acid.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The percentage by mass of oxygen in water is approximately:
सही उत्तर: ग) 88.9%
Mass % of O = 16/18 × 100 ≈ 88.9%. 11.1% is the percentage of hydrogen.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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