The number of neutrons equals 197 minus 79, which is 118. In an electrically neutral atom, the number of electrons equals the number of protons, so there are 79 electrons.
An atom has 79 protons and a mass number of 197. Calculate (i) the number of neutrons and (ii) the number of electrons.
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The mass number represents the sum of protons and neutrons within the nucleus. Subtracting 79 protons from the mass number 197 gives 118 neutrons. Since an atom is electrically neutral, the total count of negatively charged electrons must equal the total count of positively charged protons. Therefore, this neutral atom contains 79 electrons orbiting its central nucleus.
For more NCERT Solutions of Class 9 Science Exploration Chapter 8 Journey Inside the Atom Question Answer (2026-27)
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