Atomic number stays 12 since proton count is unchanged. Atomic mass increases slightly because the orbiting particles are heavier. Mass number remains 24 since nuclear nucleons are unchanged. Overall charge remains zero.
In an atom, there are 12 protons and 12 neutrons in the nucleus. Now, imagine that all the electrons are replaced with some hypothetical particles that have the same charge as electrons but are 500 times heavier. What effect will this replacement have on the atom’s: (i) Atomic number (ii) Atomic mass (iii) Mass number (iv) Overall charge
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The atomic number remains 12 because it depends solely on protons in the nucleus. Atomic mass increases slightly because twelve particles 500 times heavier than electrons add noticeable extra mass. Mass number remains exactly 24 because it counts only protons and neutrons in the nucleus. Overall charge remains neutral at zero because the hypothetical particles retain identical negative charge to electrons.
For more NCERT Solutions of Class 9 Science Exploration Chapter 8 Journey Inside the Atom Question Answer (2026-27)
https://www.tiwariacademy.com/ncert-solutions/class-9/science/exploration-chapter-8/