रसायन विज्ञान – Chemistry MCQ
रसायन विज्ञान – कृषि/वन प्रवेश
Chemistry · Agriculture, Veterinary & Forestry Entrance · ३९७ प्रश्न
३९७ 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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A solution has a pH value of 8. What is the concentration of hydrogen ions (H⁺) in this solution?
सही उत्तर: ख) 10⁻⁶ M
pH is defined as -log[H⁺]. Therefore, if pH = 8, then [H⁺] = 10⁻⁸ M. This concentration represents the acidic strength of the solution.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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What is the primary purpose of adding an acid (like hydrochloric acid) to a soil sample during chemical analysis?
सही उत्तर: ख) To neutralize alkaline soils and adjust pH levels.
Acidification is often used in soil testing to determine the initial pH. Neutralizing alkaline soils with an acid (like HCl) brings the pH closer to neutrality, allowing accurate measurement of other parameters such as phosphate and potassium concentrations. Adding acid does not directly affect organic matter solubility or nutrient uptake.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The process of dissolving a solid ionic compound in water results in the formation of:
सही उत्तर: घ) Hydration shells around the ions, stabilizing their dispersed state.
When an ionic compound like calcium chloride dissolves, water molecules surround the individual calcium and chloride ions, forming hydration shells. These shells stabilize the ions and prevent them from recombining into a solid crystal. The other options describe incorrect mechanisms of dissolving.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Which of the following statements accurately describes the role of acids and bases in fertilizer solutions?
सही उत्तर: ख) B. Bases neutralize acidity in soil, facilitating nutrient uptake by plants, while acids provide essential micronutrients.
The correct answer is B because it accurately describes the function of bases in neutralizing soil acidity and facilitating nutrient uptake – a fundamental role in fertilizer solutions. Option A misrepresents the roles of acids and bases; C overstates their equal contributions; and D focuses on a specific, less central mechanism.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The process of converting a solid reactant directly into gaseous products upon heating is called:
सही उत्तर: घ) Reduction
This describes decomposition reactions where heat energy causes the breaking down of a compound into simpler substances, often releasing gases. Neutralization involves acid-base reactions, combustion relates to burning with oxygen, and reduction refers to gaining electrons.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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What is the chemical formula for copper(II) oxide?
सही उत्तर: ख) Cu₂O
Copper(II) oxide contains two oxygen atoms bonded to one copper atom. The Roman numeral (II) indicates that the copper ion has a +2 charge. Options 2, 3 and 4 are incorrect combinations of elements reflecting varying oxidation states.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The pH of a solution prepared by dissolving 1 gram of anhydrous sodium carbonate (Na₂CO₃) in water is approximately:
सही उत्तर: ख) 7
Sodium carbonate is a basic salt. When dissolved in water, it hydrolyzes to form hydroxide ions (OH⁻), increasing the pH above 7. Options 13 and 12 are too high – the hydrolysis isn’t complete and produces less OH-. Option 7 would be correct for a neutral salt.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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What is the primary function of hydrochloric acid (HCl) in the process of nitrification carried out by soil bacteria?
सही उत्तर: ख) B. To protonate organic matter, making nitrogen more available
Option B is correct because HCl’s role in nitrification is to protonate organic matter, thus liberating ammonium ions (NH₄⁺), which are then converted to nitrate by nitrifying bacteria. Options A and C describe other processes related to nitrogen cycling; option D incorrectly states a function of acid.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Sulphuric acid is manufactured on a large scale by the contact process, which involves oxidation of SO₂ to SO₃ with vanadium pentoxide catalyst.
सही उत्तर: क) burning sulfur directly
The contact process uses vanadium pentoxide as a catalyst to facilitate the conversion of sulfur dioxide (SO₂) to sulfur trioxide (SO₃), which is then used to produce concentrated sulfuric acid.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Which of the following best describes the role of oxidation states in predicting reaction stoichiometry?
सही उत्तर: ख) The sum of oxidation states for all atoms in a molecule or ion is equal to zero.
In redox reactions, the principle of conservation of mass requires that the sum of the oxidation states of all atoms must remain constant during the reaction (the total oxidation state is always 0). This concept allows for efficient stoichiometric calculations and balancing. Options 2 & 3 are partially correct but do not explain how oxidation states are used in balancing. Option 4 incorrectly asserts a lack of relevance.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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