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 H–O–H bond angle in a water molecule is about:
सही उत्तर: ख) 104.5°
Two lone pairs on oxygen compress the bond angle below the tetrahedral value of 109.5° to about 104.5°. 109.5° is the angle in CH₄, which has no lone pairs.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Amino acids in a protein are joined together by:
सही उत्तर: घ) Peptide bonds
A peptide bond (–CO–NH–) forms between the carboxyl group of one amino acid and the amino group of another. Glycosidic bonds link sugar units in carbohydrates.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The volume occupied by 2 moles of an ideal gas at STP (taking molar volume as 22.4 L) is:
सही उत्तर: घ) 44.8 L
One mole of an ideal gas occupies 22.4 L at STP, so 2 mol occupy 2 × 22.4 = 44.8 L. 11.2 L is the volume of half a mole.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Froth flotation is used mainly for concentrating:
सही उत्तर: घ) Sulphide ores
Sulphide ore particles are wetted by oil and carried up in the froth while gangue sinks in water. Gold is often concentrated by amalgamation or cyanide leaching instead.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The rule stating that electrons occupy degenerate orbitals singly with parallel spins before pairing is:
सही उत्तर: ग) Hund's rule
Hund's rule of maximum multiplicity describes filling of degenerate orbitals. The Pauli principle says no two electrons in an atom can have all four quantum numbers the same.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The number of neutrons in an atom of ²³⁸₉₂U is:
सही उत्तर: घ) 146
Neutrons = mass number − atomic number = 238 − 92 = 146. 92 is the number of protons.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Heating ethanol with excess concentrated H₂SO₄ at about 443 K (170 °C) mainly gives:
सही उत्तर: घ) Ethene
Concentrated H₂SO₄ dehydrates ethanol intramolecularly at 443 K to give ethene. At a lower temperature (about 413 K) with excess ethanol, diethyl ether forms instead.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Alkaline hydrolysis of fats or oils with NaOH to give soap and glycerol is called:
सही उत्तर: ख) Saponification
Saponification is the base hydrolysis of triglyceride esters, producing sodium salts of fatty acids (soap) and glycerol. Hydrogenation converts oils into solid fats (vanaspati).
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The oxidation state of sulphur in H₂SO₄ is:
सही उत्तर: क) +6
2(+1) + x + 4(−2) = 0 gives x = +6. Sulphur is +4 in SO₂ and H₂SO₃.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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In soil, the conversion of ammonium (NH₄⁺) into nitrate (NO₃⁻) by bacteria is called:
सही उत्तर: ख) Nitrification
Nitrosomonas oxidises NH₄⁺ to NO₂⁻ and Nitrobacter oxidises NO₂⁻ to NO₃⁻; together this is nitrification. Denitrification reduces nitrate back to N₂ gas.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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