Which of the following is not isotopic pair? — Nuclear Chemistry and Radioactivity Chemistry Question

💡 Solution & Explanation

Step 1 - The Decay Series from Passage $$A \xrightarrow{-\alpha} B \xrightarrow{-\alpha} C \xrightarrow{-\beta^-} D \xrightarrow{-\beta^-} E \xrightarrow{-\alpha} F \xrightarrow{-\beta^-} G \xrightarrow{-\alpha} H$$ Step 2 - Track Atomic Numbers (Z) Starting with $Z_A$ as a reference: | Nuclide | After | $Z$ | |---------|-------|-----| | A | — | $Z_A$ | | B | $-\alpha$ | $Z_A - 2$ | | C | $-\alpha$ | $Z_A - 4$ | | D | $-\beta^-$ | $Z_A - 3$ | | E | $-\beta^-$ | $Z_A - 2$ | | F | $-\alpha$ | $Z_A - 4$ | | G | $-\beta^-$ | $Z_A - 3$ | | H | $-\alpha$ | $Z_A - 5$ | Step 3 - Check Each Option for Being Isotopes Isotopes have the **same atomic number (Z)** but different mass numbers. - **(A) A and D**: $Z_A$ vs $Z_A - 3$ → **Different Z** → NOT isotopes. ✓ (This is the answer.) - **(B) B and E**: $Z_A - 2$ vs $Z_A - 2$ → **Same Z** → Isotopes. - **(C) C and F**: $Z_A - 4$ vs $Z_A - 4$ → **Same Z** → Isotopes. - **(D) D and G**: $Z_A - 3$ vs $Z_A - 3$ → **Same Z** → Isotopes. $$\boxed{\text{Answer: A — A and D are NOT isotopes (they have different Z values)}}$$