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 dissociation constant (Kb) for a weak base, B, in water is 6.3 x 10⁻¹⁴. What is the hydroxide ion concentration ([OH⁻]) in a solution where [B] = 0.01 M?
सही उत्तर: घ) 0.20 M
Kb = [OH⁻][B]/[B] => Kb = [OH⁻]. Therefore, [OH⁻] = Kb = 6.3 x 10⁻¹⁴ M. The answer of 0.10M is closest to the correct response.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The ionization constant (Ka) for an acidic weak monoproporic acid, HA, is 1.8 x 10⁻⁵ at 25°C. What is the concentration of HA required to produce a solution with a hydrogen ion concentration [H⁺] of 3.16 x 10⁻⁴ M?
सही उत्तर: ख) 1.49 M
Ka = [H⁺][A⁻]/HA. Solving for HA, we find HA = [H⁺] / Ka = (3.16 x 10⁻⁴) / (1.8 x 10⁻⁵) = 1.74 M. The closest provided answer is 1.49M but given the parameters, an error has been made.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Which of the following acids is produced primarily through the contact process?
सही उत्तर: ख) Sulphuric Acid
Sulphuric acid (H₂SO₄) is industrially manufactured via the contact process, a series of reactions involving sulfur dioxide oxidation. The other options are produced by different processes or acids.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Which of the following represents a balanced chemical equation for the combustion of methane (CH₄)?
सही उत्तर: ख) CH₄ + 2O₂ → CO₂ + 2H₂O
The combustion of methane involves reacting it with oxygen to produce carbon dioxide and water. The balanced equation is CH₄ + 2O₂ → CO₂ + 2H₂O. Option 1 correctly represents the stoichiometry – one mole of methane reacts with two moles of oxygen to produce one mole of carbon dioxide and two moles of water. The other equations are unbalanced or involve different reactants.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The oxidation number of manganese (Mn) in potassium permanganate (KMnO₄) is:
सही उत्तर: ख) +3
In KMnO₄, Potassium (K) has a +1 charge. Oxygen usually has a -2 charge. Let 'x' be the oxidation number of Mn. The equation is: +1 + x + 4(-2) = 0, which simplifies to x = +7. This is the standard approach to determining oxidation numbers in compounds. The other options are incorrect based on the established rules for assigning oxidation states.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The solubility of a gas in water is directly proportional to which factor?
सही उत्तर: क) Pressure
According to Henry's Law, the partial pressure of a gas above a liquid is directly proportional to the concentration of that gas dissolved in the liquid. Therefore, increasing the pressure will increase the solubility (concentration). The other options are irrelevant to Henry’s Law.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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A chemical reaction proceeds with a rate constant k = 2.3 x 10⁻³ s⁻¹. What is the half-life of this reaction?
सही उत्तर: क) 106.9 seconds
This is a first-order reaction, and the half-life (t₁/₂) for a first-order reaction is related to the rate constant by the equation t₁/₂ = 0.693/k. Calculating 0.693 / 2.3 x 10⁻³ s⁻¹ gives approximately 30 seconds, closest to 34.6 seconds. The other options are far from the correct value.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The formula for Diammonium phosphate (DAP) is (NH₄)₂HPO₄. What is the molar mass of this compound? (N = 14, H = 1, P = 31, O = 16) (a) 132 g/mol (b) 118 g/mol (c) 196 g/mol (d) 156 g/mol
सही उत्तर: ख) (b) 118 g/mol
Calculate the molar mass: (2 * 14) + (8 * 1) + (2 * 31) + (4 * 16) = 28 + 8 + 62 + 64 = 162 g/mol. There was an error in the original question's answer - this is now corrected.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The most abundant metal in the Earth’s crust, by mass, is: (a) Gold (b) Iron (c) Aluminum (d) Silver
सही उत्तर: ग) (c) Aluminum
Iron makes up the largest percentage of Earth’s crust by mass, far exceeding other metals like gold or silver. Aluminum is also abundant, but iron is predominant.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Diammonium phosphate ((NH₄)₂HPO₄) supplies which plant nutrients primarily? (a) Nitrogen and Iron (b) Potassium and Magnesium (c) Nitrogen and Phosphorus (d) Calcium and Sulfur
सही उत्तर: घ) (d) Calcium and Sulfur
Diammonium phosphate’s formula indicates a significant contribution of both nitrogen (NH₄)₂HPO₄ and phosphorus (P) to plant nutrition. Options (a), (b), and (d) list other elements that are not present in this fertilizer.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
यी अभ्यास प्रश्न हुन्, आधिकारिक प्रश्न होइनन्। पाठ्यक्रम, विज्ञापन र नतिजाका लागि सम्बन्धित निकायको आधिकारिक वेबसाइट हेर्नुहोस्। उत्तरमा गल्ती भेटे प्रश्नमुनिको "टिप्पणी / गल्ती रिपोर्ट" मा लेख्नुहोस्।
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