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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The chemical formula for glucose (शुर्कित खुजली) is C₆H₁₂O₆. What is the valency of carbon in this molecule? (C₆H₁₂O₆ को रासायनिक सूत्र कार्बन अणुमा यसको क्यावेलिटी के हो?
सही उत्तर: ख) +3
Carbon has a valency of +4 because it forms four covalent bonds with other atoms, primarily oxygen. The other options are incorrect as they do not reflect the standard oxidation state of carbon in organic molecules.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The decomposition of hydrogen peroxide (H₂O₂) catalyzed by manganese dioxide (MnO₂) results in the formation of water and oxygen gas. Which statement best describes this process?
सही उत्तर: क) An exothermic reaction releasing heat.
The decomposition of hydrogen peroxide catalyzed by manganese dioxide is an exothermic reaction, meaning it releases heat. Options B, C, and D describe different types of reactions.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The pH of a solution is 5. What is the hydrogen ion concentration ([H⁺]) of that solution?
सही उत्तर: क) 1 x 10⁻⁵ M
pH is defined as -log[H⁺]. Therefore, if pH = 5, then [H⁺] = 10⁻⁵ M. The other options represent incorrect hydrogen ion concentrations.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Which of the following best describes the process of neutralization in chemistry?
सही उत्तर: ग) C The combination of an acid and a base to form salt and water.
Neutralization is precisely defined as the reaction between an acid and a base, resulting in the formation of salt and water. Options A, B, and D describe different chemical reactions, not neutralization.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The molar mass of glucose (C₆H₁₂O₆) is approximately 180 g/mol. If 27 g of glucose is dissolved in water, what is the concentration of the solution in mol/L?
सही उत्तर: क) 0.1 M
The calculation involves dividing the number of moles of glucose (calculated from its mass) by the volume of the solution. Option 0.2 M is correct because 27 g / 180 g/mol = 0.15 mol. The other options are incorrect as they calculate different molarities.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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A reaction has a rate constant k = 0.05 s⁻¹. What is its half-life?
सही उत्तर: घ) 9.7 s
For a first order reaction, the relationship between rate constant and half-life is given by: t₁/₂ = 0.693 / k. Substituting the value of k gives us approximately 19.3 seconds.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Single superphosphate is manufactured commercially by reacting rock phosphate with phosphoric acid and calcium hydroxide. What is the MAIN purpose of adding phosphoric acid to the reaction?
सही उत्तर: ग) To stabilize the crystalline structure of the phosphate minerals.
Phosphoric acid provides a source of phosphate ions (H₂PO₄⁻) necessary to react with the calcium from calcium hydroxide to form the soluble calcium phosphate that constitutes the fertilizer component. The other options describe secondary reactions or stabilization attempts.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Bleaching powder (Calcium Hypochlorite) is commonly added to drinking water supplies to control bacterial growth. Its primary action relies on which chemical process?
सही उत्तर: घ) Formation of a protective film over the water’s surface.
Bleaching powder contains hypochlorite ions (OCl⁻) which are strong oxidizing agents. These oxidize and destroy the cell walls and proteins of microorganisms, effectively killing or inactivating them. The other options describe different disinfection methods.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Which of the following elements is predominantly found at the central core (heme group) of chlorophyll molecules, crucial for absorbing light energy?
सही उत्तर: ग) Magnesium (Mg)
Chlorophyll contains a magnesium ion (Mg²⁺) at its center. This central metal ion is essential for the molecule's ability to absorb light energy, specifically in the red and blue wavelengths of the visible spectrum. The other options are not involved in the core structure.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The Haber-Bosch process for ammonia synthesis is represented by the equation: N₂(g) + 3H₂(g) ⇌ 2NH₃(g). Given that this reaction has a negative ΔH, what adjustment to the conditions would MOST effectively increase the yield of ammonia?
सही उत्तर: घ) Removing ammonia from the system.
A negative enthalpy change indicates an exothermic reaction. To shift the equilibrium towards product formation (ammonia), a decrease in temperature is most effective as it favors the forward reaction according to Le Chatelier's principle. Increased pressure also pushes for products but a catalyst will speed up BOTH reactions equally.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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