Correct Answer: A. An electron<\/strong><\/p>\n\n\n\n The electron has the smallest mass among the options listed. In atomic structure, three fundamental particles make up atoms: protons, neutrons, and electrons. Each of these has a distinct mass, measured in atomic mass units (amu) or kilograms.<\/p>\n\n\n\n An electron<\/strong> has a mass of approximately 9.109 \u00d7 10\u207b\u00b3\u00b9 kilograms<\/strong>, which equals about 0.00054858 amu<\/strong>. This is significantly lighter than either a proton or a neutron.<\/p>\n\n\n\n A proton<\/strong> has a mass of approximately 1.6726 \u00d7 10\u207b\u00b2\u2077 kilograms<\/strong>, or 1.007276 amu<\/strong>. A neutron<\/strong> is slightly heavier, with a mass of around 1.6750 \u00d7 10\u207b\u00b2\u2077 kilograms<\/strong>, or 1.008665 amu<\/strong>. Both are over 1,800 times more massive than the electron.<\/p>\n\n\n\n An atomic nucleus<\/strong> is made up of protons and neutrons. Therefore, its mass is the combined total of all the protons and neutrons it contains, making it far heavier than either a single proton, neutron, or electron. Even the smallest stable nucleus\u2014hydrogen-1, which contains only a single proton\u2014has more mass than an electron.<\/p>\n\n\n\n Due to its extremely small mass, the electron contributes very little to the total mass of an atom. The bulk of atomic mass is located in the nucleus, which holds the protons and neutrons. Electrons, although vital for chemical bonding and electrical properties, are essentially negligible in terms of mass contribution.<\/p>\n\n\n\n Thus, in comparison to the proton, neutron, and atomic nucleus, the electron is the lightest particle, making Option A<\/strong> the correct answer.<\/p>\n\n\n\n Which of the following has the smallest mass? A. An electron B. An atomic nucleus C. A proton D. A neutron The Correct Answer and Explanation is: Correct Answer: A. An electron The electron has the smallest mass among the options listed. In atomic structure, three fundamental particles make up atoms: protons, neutrons, and electrons. 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