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How many neutrons, protons and nucleons respectively is the ²⁰⁶₈₂Pb nucleus made up of ?

Asked in GSEB Board March 2020 (old course) · Composition, isotopes and isobars

• (1) 206, 82, 288
• (2) 82, 206, 288
• (3) 82, 124, 206
• (4) 124, 82, 206

Step-by-step solution

Why the other options are wrong

• (1) 206 is the nucleon number, not the neutron count, and 206+82=288 is not the number of nucleons either — the mass number already counts them all.
• (2) This puts the mass number in the neutron slot and adds the two numbers for a third. Neutrons are A-Z=206-82=124.
• (3) 82, 124, 206 is protons, neutrons, nucleons — the right three numbers, but this question asks for the neutrons first.

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