Chemistry

Question Analysis
This question involves reverse calculation of atomic number from mass number/neutrons, neutron count for a second isotope, element identification, and isotope naming.
The main focus is on applying the mass number formula ( ) in reverse and across multiple isotopes of the same element.

Key Concept Explanation
Mass number formula: (atomic number/protons) + (neutrons) → .
Same element → same atomic number for both isotopes; heavier isotope neutron count = mass number - atomic number.

Step-by-Step Solution
1. Atomic number ( ) = lighter isotope mass number - neutrons = 63 - 34 = 29.
2. Heavier isotope neutrons = 65 - 29 = 36.
3. Element with

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