Concept:Isotopes are variants of a specific element. Because they belong to the same element, their fundamental chemical identity (protons) remains untouched, but their nuclear weight varies.
Formula:$$ \text{Mass Number (A)} = \text{Protons (Z)} + \text{Neutrons (N)} $$
Solution:- By definition, isotopes of an element have the exact same atomic number (Z, number of protons) but a varying number of neutrons (N).
- Since the Mass Number is the sum of protons and neutrons, a different number of neutrons inherently results in a different Mass number.
Why other options are incorrect:- Number of electrons & Electronic configuration: Because isotopes have the same number of protons, neutral isotopes will have the exact same number of electrons and an identical electronic configuration. This is why isotopes exhibit nearly identical chemical properties.
- Crystal lattice: This is determined by electronic bonding interactions and atomic radius, not isotopic mass.
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