Isotopes of an element have
ASame mass number but different atomic number
BSame atomic number but different mass number
CDifferent number of protons in the nucleus
DDifferent number of electrons outside the atom
Answer & Solution
Correct answer: B. Same atomic number but different mass number
1. The chapter defines isotopes.
2. Isotopes share the same atomic number (same proton count).
3. They differ in neutron count, so their mass numbers differ.
4. So option A is correct.
_Source: Selina Concise Chemistry Class 8, Ch on Structure of Atom (Mistral OCR'd PDF), section on isotopes_
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