Atoms and Molecules (परमाणु एवं अणु) Ch(3) Practice Quiz in Hindi Part – 2 || Class 9 Science Practice Quizzes in English Posted on February 28, 2025February 28, 2025 by Anshul Gupta0% 0 votes, 0 avg 0 Atoms and Molecules (परमाणु एवं अणु) Ch(3)Practice Quiz in Hindi Part – 2 || Class 9 Science Practice Quizzes in English 1 / 201. What is the molar mass of the phosphorus molecule (P4)? A. 248 g/mol B. 31 g/mol C. 62 g/mol D. 124 g/mol Explanation: The molar mass of the phosphorus molecule is calculated as: 4 (atomic mass of phosphorus) = 4 (31 g/mol) = 124 g/mol.2 / 202. What is the chemical formula for aluminium oxide? A. Al2O B. AlO C. Al2O3 D. AlO3 Explanation: The chemical formula for aluminium oxide is Al2?O3?, as aluminium has a valency of 3 and oxygen has a valency of 2. 3 / 203. What is the chemical formula for calcium hydroxide? A. CaOH2 B. Ca2(OH) C. Ca(OH)2 D. CaOH Explanation: The chemical formula for calcium hydroxide is Ca(OH)2?, as calcium has a valency of 2 and the hydroxyl group (OH) has a valency of 1. 4 / 204. What is the valency of oxygen? A. 4 B. 1 C. 2 D. 3 Explanation: The valency of oxygen is 2, meaning it can form two chemical bonds with other elements. 5 / 205. What is the combining power of an element called? A. Atomicity B. Valency C. Ionization energy D. Atomic mass Explanation: Valency is the combining power of an element, which determines how its atoms will combine with atoms of other elements to form compounds. 6 / 206. What is the molar mass of the sulfur molecule (S8)? A. 256 g/mol B. 128 g/mol C. 64 g/mol D. 32 g/mol Explanation: The molar mass of the sulfur molecule is calculated as: 8 (atomic mass of sulfur) = 8 (32 g/mol) = 256 g/mol.7 / 207. What is the chemical formula for magnesium chloride? A. Mg2Cl2 B. Mg2Cl C. MgCl D. MgCl2 Explanation: The chemical formula for magnesium chloride is MgCl2?, as magnesium has a valency of 2 and chlorine has a valency of 1. 8 / 208. What is the chemical formula for quicklime? A. Ca(OH)2 B. CaCl2 C. CaCO3 D. CaO Explanation: Quicklime is the common name for calcium oxide, which has the chemical formula CaO.9 / 209. What is the molecular mass of water (H2O)? A. 16 u B. 10 u C. 20 u D. 18 u Explanation: The molecular mass of water is calculated as: 2 (atomic mass of hydrogen) + 1 (atomic mass of oxygen) = 2 (1 u) + 1 (16 u) = 18 u. 10 / 2010. What is the formula unit mass of calcium chloride (CaCl2)? A. 142 u B. 71 u C. 75.5 u D. 111 u Explanation: The formula unit mass of calcium chloride is calculated as: 1 (atomic mass of calcium) + 2 (atomic mass of chlorine) = 1 (40 u) + 2 (35.5 u) = 111 u. 11 / 2011. What is the formula unit mass of a substance? A. The valency of the compound. B. The mass of a single formula unit of the compound. C. The number of formula units in a compound. D. The sum of the atomic masses of all atoms in a formula unit of a compound. Explanation: The formula unit mass is the total mass of a formula unit, which is the smallest unit of an ionic compound. 12 / 2012. What is the chemical formula for sodium carbonate? A. Na2CO3 B. Na(CO3)2 C. Na2(CO3)2 D. NaCO3 Explanation: The chemical formula for sodium carbonate is Na2?CO3?, as sodium has a valency of 1 and the carbonate group (CO3) has a valency of 2. 13 / 2013. What is the chemical formula for sodium chloride? A. Na2Cl2 B. Na2Cl C. NaCl2 D. NaCl Explanation: The chemical formula for sodium chloride, commonly known as table salt, is NaCl. 14 / 2014. What is the molar mass of hydrochloric acid (HCl)? A. 36.5 g/mol B. 37.5 g/mol C. 35.5 g/mol D. 38.5 g/mol Explanation: The molar mass of hydrochloric acid is calculated as: 1 (atomic mass of hydrogen) + 1 (atomic mass of chlorine) = 1 (1 g/mol) + 1 (35.5 g/mol) = 36.5 g/mol.15 / 2015. Which of the following is NOT a polyatomic ion? A. Chloride (Cl−) B. Hydroxide (OH−) C. Ammonium (NH4+) D. Nitrate (NO3−) Explanation: Chloride is a monatomic ion, consisting of a single chlorine atom with a negative charge. 16 / 2016. What is the molar mass of ethyne (C2H2)? A. 28 g/mol B. 26 g/mol C. 30 g/mol D. 32 g/mol Explanation: The molar mass of ethyne is calculated as: 2 (atomic mass of carbon) + 2 (atomic mass of hydrogen) = 2 (12 g/mol) + 2 (1 g/mol) = 26 g/mol.17 / 2017. What is the molar mass of nitric acid (HNO3)? A. 67 g/mol B. 63 g/mol C. 69 g/mol D. 65 g/mol Explanation: The molar mass of nitric acid is calculated as: 1 (atomic mass of hydrogen) + 1 (atomic mass of nitrogen) + 3 (atomic mass of oxygen) = 1 (1 g/mol) + 1 (14 g/mol) + 3 (16 g/mol) = 63 g/mol.18 / 2018. What is the chemical formula for ammonium sulphate? A. NH4SO4 B. (NH4)2SO4 C. NH4(SO4)2 D. (NH4)2(SO4)2 Explanation: The chemical formula for ammonium sulphate is (NH4?)2?SO4?, as the ammonium group (NH4) has a valency of 1 and the sulphate group (SO4) has a valency of 2. 19 / 2019. What is the chemical formula for baking powder? A. NaHCO3 B. NaOH C. CaCO3 D. NaCl Explanation: Baking powder is chemically known as sodium bicarbonate or sodium hydrogen carbonate, with the formula NaHCO3?. 20 / 2020. What is the molecular mass of a substance? A. The sum of the atomic masses of all the atoms in a molecule of the substance. B. The number of atoms in a molecule of the substance. C. The valency of the substance. D. The mass of a single atom of the substance. Explanation: The molecular mass is the total mass of a molecule, calculated by adding the atomic masses of all the atoms in its chemical formula. 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