The mass number assigned to a given atomic nucleus represents the combined total of___________________?
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Answer: D. protons and neutrons in a nucleus
Explanation
The mass number of any given atomic nucleus is defined by its total nucleon count. Nucleons consist of positively charged protons and electrically neutral neutrons bound together tightly. Summing these two particle counts gives the exact integer mass number for the isotope. Protons and neutrons have very similar masses, each approximately equal to one atomic mass unit. Electrons are excluded from mass number calculations because their mass is extremely negligible. Isotopes of the same element share proton counts but differ in their total neutron counts.
Mass numbers are essential for identifying specific nuclear isotopes in chemistry and engineering calculations. Nuclear reactors require precise isotope identification to predict fission behavior and fuel longevity. Standard chemical nomenclature places the mass number as a superscript before the atomic symbol. Option B is wrong because electrons do not reside inside the nucleus and contribute virtually no mass. Option C is incorrect because it completely omits protons from the total nucleon sum. Option E is wrong because electrons are included erroneously in place of neutrons.
- Subject
- Engineering
- Category
- Mechanical Engineering
- Topic
- —
- Difficulty
- medium
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