रसायन विज्ञान (Chemistry) – Chemistry MCQ
रसायन विज्ञान (Chemistry) – CEE प्रवेश
Chemistry · Medical Entrance (CEE) – Physics, Chemistry, Biology & MAT · ४१० प्रश्न
४१० प्रश्न उपलब्ध। मोड छान्नुहोस्:
रसायन विज्ञान (Chemistry): 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 of acetone with sodium hydroxide solution followed by treatment with hydrochloric acid produces which product?
सही उत्तर: घ) Acetaldehyde
This is a classic example of the Williamson ether synthesis. Sodium hydroxide deprotonates acetone to form an enolate ion. This enolate then reacts with HCl to form ethyl methyl ketone. The other options represent different reaction pathways involving ketones or aldehydes.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Which of the following oxides of nitrogen does NOT contain any oxygen-oxygen bonds?
सही उत्तर: ग) Nitrous oxide (N₂O)
Nitric oxide (NO) is formed from the direct combination of nitrogen and oxygen without any oxygen-oxygen bond formation. The other oxides contain one or more oxygen-oxygen bonds as they are compounds of nitrogen and oxygen. Carbon Monoxide is an exception as it contains a C=O double bond.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The reaction of 1-butene with hydrogen in the presence of a catalyst gives predominantly:
सही उत्तर: क) Butane
This is a typical example of catalytic hydrogenation. The reaction proceeds via Markovnikov’s rule – hydrogen adds to the carbon with more alkyl groups attached. Butane is the saturated product formed by complete addition of H₂. The other options represent different products from partial or anti-Markovnikov additions.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Which of the following reagents can convert alkenes into alcohols? (2021)
सही उत्तर: ख) NaOH
Hydrobromic acid (HBr) is a strong acid that reacts with alkenes via an anti-Markovnikov addition to yield alcohols. The other options, while involved in chemical reactions, do not directly facilitate alkene hydration to form alcohols.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The decomposition reaction of potassium chlorate (KClO₃) can be represented as 4KClO₃(s) → 3KClO₄(s) + Cl₂(g). If 20 grams of KClO₃ are heated, what mass of chlorine gas (Cl₂) will be produced? (K = 39.1 g/mol, Cl = 35.5 g/mol, O = 16.0 g/mol)
सही उत्तर: ख) 4.9g
The balanced equation shows a 1:1 molar ratio between KClO₃ and Cl₂. We calculate the moles of KClO₃ (20 g / 39.1 g/mol = 0.512 mol). Then, using the mole ratio, we get 0.512 mol of Cl₂. Finally, we convert to grams (0.512 mol * 35.5 g/mol = 18.1 g). The most tempting incorrect answer is '7.8g' as it’s close but based on a misunderstanding of the reaction stoichiometry.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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What is the molar mass of H₂SO₄ (sulfuric acid)?
सही उत्तर: ख) 100 g/mol
The molecular formula for sulfuric acid is H₂SO₄. To calculate the molar mass, we add the atomic masses of each element: (2 × 1) + (32) + (4 × 16) = 98 g/mol. This is a standard calculation involving the periodic table.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The pH of a 0.1 M solution of acetic acid (CH₃COOH) is 4.76. What is the Ka value for acetic acid?
सही उत्तर: क) 1.8 × 10⁻⁵
Ka is calculated using the formula pH = -log[H⁺]. Therefore, [H⁺] = 10^(-pH) = 10^(-4.76) ≈ 1.9 × 10⁻⁵. Then Ka = [H⁺]/([CH₃COOH]) = (1.9×10⁻⁵)/(0.1) = 1.9 x 10^-4. The closest value is 2.9 x 10⁻⁴.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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What is the chemical formula for iron(III) oxide, formed by the reaction of iron with oxygen?
सही उत्तर: क) Fe₂O₃
Iron(III) oxide is represented as Fe₂O₃. It’s formed through oxidation of iron to a +3 state, and this is the most stable form under standard conditions. The other options represent different stoichiometries that are not consistent with the reaction.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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What is the primary chemical basis for the use of hydrogen peroxide (H₂O₂) as a disinfectant?
सही उत्तर: ग) It decomposes into oxygen and water, producing a toxic environment for microorganisms
Hydrogen peroxide decomposes into water and oxygen. The released oxygen is highly toxic to most microorganisms, effectively killing them. Options A, B and C are incorrect as they describe chemical reactions that don't explain the disinfectant properties.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Which of the following statements best describes the effect of increasing the surface area of a solid reactant in a heterogeneous reaction?
सही उत्तर: ग) It increases the reaction rate proportionally
Increasing the surface area provides more contact between the reactants and catalyst (if present), significantly increasing the reaction rate. Options A and B are incorrect as surface area directly influences reaction kinetics. Option D is partially true, but doesn't fully explain why it increases the rate; a larger surface area leads to more collisions.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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