alleryStart learning →The discovery of the neutron explained isotopes because isotopes differ in:
ANeutron number only
BProton number only
CElectron number only
DBoth proton and electron
Answer & Solution
Correct answer: A. Neutron number only
1. Isotopes are chemically identical yet differ in mass, which needs explaining.
2. Chemical behaviour is set by the number of protons and therefore of electrons.
3. Isotopes differ in mass because they have different numbers of neutrons, but they are chemically identical because they have the same number of protons.
4. Changing the proton number would change the element entirely.
_Source: OpenStax Chemistry 2e (CC BY 4.0), Ch 2 'Atoms, Molecules, and Ions', sections 2.1-2.6_
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