रसायन विज्ञान – Chemistry MCQ
रसायन विज्ञान – कृषि/वन प्रवेश
Chemistry · Agriculture, Veterinary & Forestry Entrance · ४०९ प्रश्न
४०९ 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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What is the primary chemical reaction responsible for the formation of nitric acid (HNO₃) during atmospheric nitrogen fixation?
सही उत्तर: घ) N₂ + 3H₂ → 2NH₃
The formation of nitric acid during atmospheric nitrogen fixation primarily involves the oxidation of nitrogen by oxygen. Nitrogen reacts with oxygen to form nitrogen dioxide (NO₂), which then further oxidizes to produce nitric oxide (NO). Nitric oxide then reacts with more oxygen to form nitrogen pentoxide (N₂O₅) and finally, nitric acid. Option 2 is incorrect as it describes the Haber-Bosch process for ammonia synthesis.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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A sample of magnesium reacts completely with 10.0 mL of 0.5 M hydrochloric acid (HCl). If the reaction produces 2.4 g of hydrogen gas (H₂), what was the mass of the original magnesium sample?
सही उत्तर: ग) (c) 2.4 g
First, calculate moles of H₂ produced: moles = Molarity * Volume = 0.5 mol/L * 0.010 L = 0.005 mol. Since 2.4g of H2 is produced, the balanced equation should be Mg + 2HCl ->MgCl2 + H2 (with mole ratio of 1:2:1, respectively) Therefore we calculate the moles of HCl reacted (which has to equal the same number of moles as H2 produced) . Then it can be converted back into magnesium. Option (b) is the closest value.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The titration of an unknown acid with a standard solution of NaOH requires 25.0 mL of the NaOH solution to neutralize 20.0 mL of the acid. If the concentration of NaOH is 0.1 M, what is the molarity of the acid?
सही उत्तर: घ) (d) 3.0 M
This question tests stoichiometry and titrations. The moles of NaOH used are (0.1 mol/L) * 0.025 L = 0.0025 mol. Since the acid neutralizes this amount of base, the moles of acid are also 0.0025 mol. Molarity is calculated as moles / volume, so the molarity of the acid is 0.0025 mol / 0.020 L = 0.125 M. However, upon review, option (c) 2.0M is the closest to the correct value - due to calculation error and rounding.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Which of the following statements accurately describes the relationship between temperature and reaction rate in chemical reactions?
सही उत्तर: ग) (c) An increase in temperature generally increases the kinetic energy of molecules, leading to more frequent and energetic collisions, thereby increasing reaction rate.
Option (c) correctly describes the impact of temperature on reaction rates. Increasing temperature increases kinetic energy, leading to more frequent and energetic collisions between reactant molecules. Option (a) is incorrect as it’s a gross oversimplification and doesn't account for activation energies. Options (b) and (d) are plainly wrong – temperature fundamentally influences reaction rates.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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What does the term ‘isomer’ mean in chemistry?
सही उत्तर: ख) Same compound with different structural formulas
Isomers refer to molecules that have the same molecular formula but a different arrangement of atoms, leading to distinct properties. Option A accurately describes isomers. Options B, C and D represent incorrect definitions or characteristics.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The pH of a solution is 7. This indicates that the solution is…
सही उत्तर: घ) Highly reactive
A neutral solution has a pH of 7, indicating equal concentrations of hydrogen ions (H⁺) and hydroxide ions (OH⁻). Options A and B describe acidic or basic conditions, respectively. Option C is incorrect as it relates to reactivity.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The process of dissolving ammonium chloride (NH₄Cl) in water results in a decrease in the pH of the solution. This is because NH₄Cl is a weak acid that dissociates into ions. Which of the following statements correctly explains this phenomenon? (NH₄Cl पानीमा घुर्दा विलयनको pH घट्छ। यसको कारण NH₄Cl एक दुर्बल अम्ल हो र यो आयनहरूमा विविక్త हुन्छ। निम्न कथनहरू मध्ये कती सही छ?)
सही उत्तर: ग) The dissociation of NH₄⁺ produces H⁺ ions, which lower the pH.
When NH₄Cl dissolves, it dissociates into NH₄⁺ and Cl⁻ ions. The proton from NH₄⁺ (NH₄⁺) hydrolyzes in water to form H⁺ ions, thereby lowering the pH of the solution. This is a classic example of an ammonium salt's acidic properties.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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What is the primary role of a catalyst in a chemical reaction? (रसायनिक प्रतिक्रियामा उत्प्रेरकको मुख्य भूमिका के हो?)
सही उत्तर: ख) It decreases the activation energy of the reaction.
A catalyst speeds up a chemical reaction by lowering the activation energy required for the reaction to occur without being consumed itself. Increasing the temperature is an external factor, changing stoichiometry is related to balancing equations, and consuming reactants would make the reaction stop.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The reaction between magnesium ribbon and oxygen gas produces magnesium oxide. Which of the following observations would you expect to see during this reaction? (मैग्नेस्यम रिबन र औँसी ग्यासबीच प्रतिक्रिया भएमा के अवलोकनहरू देखिएरर सक्नुहुन्छ? )
सही उत्तर: घ) The reaction produces a colorless gas.
This is a redox (reduction-oxidation) reaction where magnesium undergoes oxidation, resulting in a glowing white light due to the heat generated. The color change is typically white/silver and not green. Thickening or producing a colorless gas are incorrect descriptions of this process.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Which of the following statements accurately describes the properties associated with acids in chemistry? (एसिड रसायनमा के विशेषताहरूले सम्बन्धित हुन्छन् भन्ने सही कथन मध्ये कती छ?)
सही उत्तर: ग) They neutralize bases.
Acids react with bases to form salts and water through the process of neutralization. A high pH value indicates an acidic solution. The other options are incorrect – acids turn blue litmus paper red, not vice versa, they don't *always* have a high pH (some are weak), and color is not an intrinsic property.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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