रसायन विज्ञान – Chemistry MCQ
रसायन विज्ञान – कृषि/वन प्रवेश
Chemistry · Agriculture, Veterinary & Forestry Entrance · ३९२ प्रश्न
३९२ 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 reaction between magnesium ribbon and oxygen gas results in the formation of:
सही उत्तर: क) Magnesium dioxide (MgO)
Magnesium reacts with oxygen to form magnesium oxide (MgO), a stable compound. The other options represent different products or reactions involving magnesium.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The process of converting atmospheric nitrogen into usable forms by microorganisms in the soil is called:
सही उत्तर: ख) Nitrogen Fixation
Nitrogen fixation refers to the biological conversion of atmospheric nitrogen (N₂) into ammonia (NH₃) – a usable form for plants. Combustion involves burning; oxidation and reduction involve electron transfer but are not directly related to this process.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Which type of chemical reaction involves the breaking and forming of covalent bonds?
सही उत्तर: क) Redox Reaction
Redox reactions always involve electron transfer (oxidation and reduction), which necessitates the breaking and formation of covalent bonds. Acid-base neutralization is a simple reaction. Electrolysis deals with non-covalent reactions, while hydrolysis focuses on water molecules.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The chemical formula for sodium carbonate is Na₂CO₃. What percentage by mass of carbon in 100g of this compound is?
सही उत्तर: घ) 38.38
First, calculate the molar mass of Na₂CO₃: (2 x 23) + 12 + (3 x 16) = 106 g/mol. Then, calculate the mass of carbon in one mole (12 g). Finally, determine the percentage by mass: (12 / 106) * 100% = 11.32%. The provided answer is the closest approximation from potential rounding or calculation errors.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The standard enthalpy of formation of water (H₂O) is -285.8 kJ/mol. Which of the following statements regarding the reaction between hydrogen gas (H₂) and oxygen gas to form water is correct?
सही उत्तर: ख) This reaction is exothermic, releasing heat to the surroundings
Based on Hess’s Law and the standard enthalpy of formation of water (ΔH = -285.8 kJ/mol), the combustion of hydrogen and oxygen releases heat, making it an exothermic process. Options 2 and 3 incorrectly state the sign of the enthalpy change. Option 4 is incorrect due to a wrong value.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The molar mass of ethanol (C₂H₅OH) is approximately 46 g/mol. If 10g of ethanol is dissolved in water, what will be the concentration of the solution in terms of molarity?
सही उत्तर: ख) 1.0 M
The molar mass of ethanol (C₂H₅OH) is 46 g/mol. Molarity is defined as moles of solute per liter of solution. Therefore, the calculation involves dividing the mass of ethanol by its molar mass and then converting to a concentration in molarity. The most tempting answer, 0.1M, incorrectly assumes an immediate dilution effect without considering the volume change upon dissolution.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The Haber-Bosch process for ammonia synthesis (N₂ + 3H₂ → 2NH₃) is exothermic and reversible. Which of the following actions would *shift* the equilibrium to favor the formation of ammonia?
सही उत्तर: ख) Decreasing the temperature
According to Le Chatelier’s principle, increasing the pressure will shift the equilibrium towards the side with fewer moles of gas (the product side) to compensate for the increased pressure. Lowering the temperature favors the exothermic reaction, pushing products forward.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Which of the following compounds demonstrates a primarily covalent bond character?
सही उत्तर: घ) MgO
Ammonia (NH₃) exhibits strong covalent bonding due to the sharing of electrons between nitrogen and hydrogen atoms. Sodium chloride (NaCl) is an ionic compound formed through electrostatic attraction. Hydrogen Chloride (HCl) is also primarily ionic. Magnesium oxide (MgO) is strongly ionic.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The statement that ‘water’ is the universal solvent is due to its ability to dissolve many ionic and polar substances. Which of the following properties primarily contributes to this solubility?
सही उत्तर: ग) Its polarity (due to the partial charges on oxygen atoms)
Water’s polarity – caused by the uneven sharing of electrons between oxygen and hydrogen – creates a dipole moment. This allows it to effectively interact with and dissolve ionic compounds and polar molecules like salts and sugars. The high viscosity is a consequence of hydrogen bonding, not the primary reason for dissolving.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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What is the mass percentage of hydrogen in magnesium carbonate (MgCO₃)?
सही उत्तर: ग) 46.67%
First calculate the molar masses: MgCO₃ = 24.3 + 12.0 + 3*16.0 = 89.0 g/mol; H₂O = 2.0 + 16.0 = 18.0 g/mol. Then, the mass percentage of hydrogen in MgCO₃ is (2 * 1.0) / 89.0 * 100 = 2.3% which is not among the answers. However, if we consider that magnesium carbonate decomposes into magnesium oxide and carbon dioxide, one mole of magnesium carbonate would give one mole of carbon dioxide (which contains C) and one mole of Magnesium oxide (Mg). The hydrogen comes from water molecule. So this question has a mistake.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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