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 demonstrates Le Chatelier's principle?
सही उत्तर: ग) 3. Increasing the pressure on a gaseous reaction favors the side with fewer moles of gas
Le Chatelier's principle states that if a change of condition (e.g., temperature, pressure) is applied to a system in equilibrium, the system will shift in a direction that relieves the stress. Increasing the temperature favors the endothermic direction as it absorbs heat. Option 1 shows solubility decreasing with increased temperature; option 3 deals with gas volumes, and option 4 refers to common salt dissolving.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The approximate molar concentration of HCl in a solution with a pH of 3 at 25°C is:
सही उत्तर: ख) 2. 1 x 10⁻³ M
pH = -log[H⁺]. Therefore, [H⁺] = 10⁻pH = 10⁻³. So the molar concentration is 1 x 10⁻³ M. The most tempting answer, 1 x 10⁻² M, arises from incorrectly applying the pH formula with a different base.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The artificial sweetener aspartame is used only in cold foods and drinks because it: (a) Degrades rapidly at high temperatures. (b) Increases in sweetness at elevated temperatures. (c) Forms a stable complex with proteins. (d) Reacts violently with acidic solutions.
सही उत्तर: ख) (b) Increases in sweetness at elevated temperatures.
Aspartame is thermally unstable and decomposes significantly when heated. This is why it’s predominantly used in cold foods and beverages where rapid degradation isn't a major concern.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The process of converting a liquid into gas at a temperature below its boiling point is called:
सही उत्तर: घ) D. Liquefaction
Option 3, Vaporization, correctly describes the transition from a liquid to a gaseous state without reaching the boiling point. Condensation is the reverse process. Sublimation involves solid-to-gas conversion, and Liquefaction represents the opposite – gas to liquid.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The rate of reaction between hydrochloric acid (HCl) and sodium carbonate (Na₂CO₃) increases when the concentration of either reactant is increased. This is because the rate of reaction depends on the collision frequency of the reactant molecules. What is the primary reason for this dependence?
सही उत्तर: ग) C. Higher concentrations lead to more frequent collisions between HCl and Na₂CO₃ molecules, increasing the probability of a successful reaction.
Option C is correct because it accurately describes how reaction rates are affected by reactant concentration – increased concentration leads to increased collision frequency. Option A is incorrect as temperature effects are not directly linked to collision frequency in this case. Option B misrepresents the reaction mechanism; while bimolecular reactions exist, this simple acid-base reaction doesn’t necessarily require that specific mechanism. Option D suggests a non-existent intrinsic reactivity difference.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Which of the following statements regarding titration with a strong acid and a strong base is most accurate?
सही उत्तर: ख) The pH changes abruptly at the equivalence point
Titrations involving strong acids and bases result in a sharp change (indicated by a sudden shift) in pH at the equivalence point where moles of acid = moles of base. This is because the resulting solution is neutral (pH=7). The other options describe gradual changes or incorrect behavior for titrations with strong acid-base solutions.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The dissociation constant (Ka) for a weak acid, HA, in water is 1.8 x 10⁻⁵ at 25°C. What is the concentration of HA in a solution where its initial concentration is 0.1 M?
सही उत्तर: ख) 0.30 M
The dissociation reaction is HA + H₂O ⇌ H₃O⁺ + A⁻. Ka = [H₃O⁺][A⁻] / [HA]. Given Ka, we can calculate the concentration of H₃O⁺ and then use that to determine the initial concentration of HA in solution; therefore, 0.30M is the correct answer. The other options are incorrect because they do not correctly apply the definition of Ka and consider the initial concentration.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Which of the following statements correctly describes the properties of acids? (a) They are always colorless and odorless. (b) They taste bitter and slippery to the touch. (c) They readily donate protons (H⁺) in solution. (d) They are primarily used as oxidizing agents.
सही उत्तर: ग) (c) They readily donate protons (H⁺) in solution.
Option (c) is correct because acids, by definition, release hydrogen ions (protons) when dissolved in water, defining their acidic properties. Option (a) is incorrect as acids can be colored and have distinct smells depending on the acid. Option (b) describes bases, not acids. Option (d) describes oxidizing agents, not acids.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The partial pressure of oxygen in air is approximately 21%. What percentage of the total atmospheric pressure at sea level would be contributed by the nitrogen component?
सही उत्तर: क) 79%
At standard temperature and pressure (STP), the composition of air is approximately 78% Nitrogen, 21% Oxygen, and small amounts of other gases. Therefore, Nitrogen contributes roughly 78% of the total atmospheric pressure. The option '79%' is chosen as it reflects an approximate value within a reasonable range due to slight variations in conditions.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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What is the primary reason for the decreased reactivity of alcohols compared to ethers?
सही उत्तर: ख) Alcohols form stronger hydrogen bonds
Alcohols exhibit decreased reactivity due to their ability to form strong hydrogen bonds. These hydrogen bonds require energy to break, thus slowing down reaction rates. The other options are less relevant or incorrect explanations for the difference in reactivity between alcohols and ethers. Hydrogen bonding is a key characteristic of alcohol behavior.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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