Decrease in atomic number is observed during — Nuclear Chemistry and Radioactivity Chemistry Question

💡 Solution & Explanation

Step 1 - Effect of Each Decay Mode on Atomic Number (Z) Recall the decay equations: - **α decay**: $\ce{^A_Z X -> ^{A-4}_{Z-2} Y + ^4_2He}$ → $Z$ **decreases by 2** - **β⁻ decay**: $\ce{^A_Z X -> ^A_{Z+1} Y + e^- + \bar\nu_e}$ → $Z$ **increases by 1** - **β⁺ (positron) decay**: $\ce{^A_Z X -> ^A_{Z-1} Y + e^+ + \nu_e}$ → $Z$ **decreases by 1** - **Electron capture (EC)**: $\ce{^A_Z X + e^- -> ^A_{Z-1} Y + \nu_e}$ → $Z$ **decreases by 1** Step 2 - Identify Cases with Decreasing Atomic Number | Decay | Change in Z | Atomic number decreases? | |-------|------------|--------------------------| | α decay | $-2$ | **Yes** ✓ | | β⁻ decay | $+1$ | No | | Positron decay | $-1$ | **Yes** ✓ | | Electron capture | $-1$ | **Yes** ✓ | Step 3 - Evaluate Options - **(A) α decay**: $Z$ decreases by 2. **Correct.** - **(B) β decay** (β⁻): $Z$ increases by 1. Does **not** decrease. Incorrect. - **(C) positron decay**: $Z$ decreases by 1. **Correct.** - **(D) electron capture**: $Z$ decreases by 1. **Correct.** $$\boxed{\text{Answer: A, C, D}}$$