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 reactions involves a redox process?
सही उत्तर: ग) 2H₂O₂(aq) → 2H₂O(l) + O₂(g)
The reaction 2H₂O₂(aq) → 2H₂O(l) + O₂(g) is a redox process because oxygen is being oxidized (increasing its oxidation state from -2 in H₂O₂ to 0 in O₂) and hydrogen is being reduced (decreasing its oxidation state from +1 in H₂O₂ to 0 in H₂O). The other reactions are simply double displacement or neutralization.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Which of the following statements correctly describes the nature of a Bronsted-Lowry acid?
सही उत्तर: ख) A substance which donates a proton (H⁺) or its equivalent
The correct answer is 'A substance which donates a proton (H⁺) or its equivalent’ because Bronsted-Lowry acids are defined as proton donors. The other options describe incorrect characteristics or reactions related to acids.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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According to Le Chatelier’s principle, if a reversible reaction at equilibrium is subjected to increased pressure, the position of the equilibrium will shift to favor the side with fewer moles of gas. Which of the following reactions demonstrates this principle when heated?
सही उत्तर: क) N₂O₄(g) → 2NO₂(g); ΔT = 10°C
The correct answer is ‘CO(g) + H₂O(g) → CO₂(g) + H₂(g); ΔV = 50%’ because shifting the equilibrium to favor a side with fewer moles of gas (in this case, 1 mole on each side) occurs when there's a change in pressure. The other options involve changes that don't directly illustrate the principle regarding moles of gaseous reactants/products.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The decomposition of lead(II) iodide (PbI₂) is an endothermic reaction. Which statement accurately describes this process?
सही उत्तर: ग) Increasing the temperature increases the rate of decomposition
According to Le Chatelier's principle, a system at equilibrium will shift to relieve stress. In this case, increasing the temperature (adding heat) is a stress. The system responds by shifting towards the products (decomposition), thus increasing the rate of decomposition. This means decreasing temperature increases the rate.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The reaction: N₂O₅ → 4NO₂ + O₂ is reversible. At equilibrium, the concentration of N₂O₅ is 0.1 M and the concentration of NO₂ is 0.8 M. What is the value of the equilibrium constant Kp for this reaction?
सही उत्तर: घ) 16
Kp = (PNO₂)⁴ / (P(N₂O₅) * P(O₂)) We assume standard temperature and pressure. So, P(NO₂) = 0.8, P(N₂O₅) = 0.1, and P(O₂) = 0.8. Therefore, Kp = (0.8)⁴ / (0.1 * 0.8) = 4.096 / 0.08 = 51.2. This value is not among the provided options, which indicates a mistake in the question formulation or expected answer. However, we can correct it based on the logic above : Kp = (PNO₂)⁴ / (P(N₂O₅) * P(O₂)) = (0.8)^4/(0.1*0.8) = 51.2 which is closest to 51.2 and by approximation, it is closest to 51. This shows that the question cannot be answered directly, but instead of calculating Kp as above, lets look at its ratio : (PNO₂/P(N₂O₅))= (0.8/0.1) = 8. The given options clearly show there is some mistake in formulating the problem or provided answer. I'm assuming that the required answer should have been 8
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Which of the following statements correctly describes the trend in ionization energy across a period (left to right) in the periodic table?
सही उत्तर: ग) Ionization energy generally increases with increasing atomic radius
Across a period, the number of protons and electrons increase. This results in a stronger effective nuclear charge, leading to increased attraction for electrons and thus an increase in ionization energy. The option ‘Ionization energy increases with increasing atomic radius’ is incorrect because the opposite trend applies – larger atoms have weaker attraction.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The pH of a solution containing 0.1 M hydrochloric acid (HCl) and 0.2 M ammonia (NH₃) is approximately: (Ka for NH₃ = 1.8 × 10⁻⁵)
सही उत्तर: क) 0.6
The solution is a buffer solution containing HCl and NH₃. The pH is determined by the Henderson-Hasselbalch equation: pH = pKa + log([NH₃]/[HCl]). Here, pKa = -log(1.8 x 10⁻⁵) ≈ 4.74. Thus, pH = 4.74 + log(0.2/0.1) = 4.74 + log(2) ≈ 4.74 + 0.30 = 5.04. The most tempting answer, 0.6, is incorrect because it doesn't account for the initial concentrations of acid and base.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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What is the primary reason for using concentrated sulfuric acid (H₂SO₄) as a dehydrating agent in organic chemistry?
सही उत्तर: ख) Its strong oxidizing power converts alcohols to ketones and aldehydes efficiently
Option 1 is correct. Concentrated sulfuric acid's effectiveness as a dehydrating agent stems from its strong affinity for oxygen atoms – it pulls those off organic molecules (like alcohols) forming alkenes efficiently. The other options are incorrect. It doesn’t form hydrogen gas, its oxidizing power isn't the primary reason for dehydration, and it’s not a catalyst.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The decomposition of lead(II) iodide (PbI₂) upon heating produces lead monoxide (PbO) and iodine vapor (I₂). Which statement correctly describes the reaction?
सही उत्तर: क) It’s a redox reaction involving reduction of Pb²⁺ to PbO and oxidation of I⁻ to I₂
Option 0 is correct as it accurately describes the reaction – lead(II) iodide decomposes into lead monoxide and iodine vapor, reflecting changes in oxidation states (Pb²⁺ is reduced to PbO while I⁻ is oxidized to I₂). The other options are incorrect; this process is not exothermic, the reaction isn't reversible in the way presented, and doesn’t involve single electron transfer. This aligns with standard chemical knowledge regarding lead iodide decomposition.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Which of the following oxides of nitrogen is primarily responsible for the brown colour of smog?
सही उत्तर: घ) N₂O₅
Nitrogen dioxide (NO₂) absorbs light in the visible region, specifically around wavelengths that correspond to red and yellow colors, giving it a brown color. This absorption contributes to the brownish hue observed in smog. The other nitrogen oxides do not contribute significantly to the smog's coloration.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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