Atomic Structure and Isotopes: Question 8

Worked solution

Step 1: Recall the definition of isotopes

Isotopes are atoms of the same element, meaning the same proton number, with different nucleon numbers (because they have different numbers of neutrons).

Step 2: Compare the proton numbers in the table

• W and X both have proton number $17$, but different nucleon numbers ($35$ and $37$), this matches the definition of isotopes.
• Y has proton number $18$, different from all the others, so it cannot be an isotope of W, X or Z.
• Z has proton number $16$, different from all the others, so it cannot be an isotope of W, X or Y.

Why the other options are wrong

• B (W and Y): proton numbers $17$ and $18$ are different, so these are different elements, not isotopes.
• C (X and Z): proton numbers $17$ and $16$ are different, so these are different elements, not isotopes.
• D (Y and Z): proton numbers $18$ and $16$ are different, so these are different elements, not isotopes.

Final answer

• $\boxed{\text{W and X}}$ are isotopes of each other, option A.