In the fourth period of the periodic table, how many elements have one or more 4d electrons? — Periodic Table and Periodicity Chemistry Question

💡 Solution & Explanation

# Fourth Period Elements with 4d Electrons **Identify the fourth period:** The fourth period spans from $K$ (Z = 19) to $Kr$ (Z = 36). **Determine which elements have 4d electrons:** The $4d$ subshell begins filling in the **fifth period**, not the fourth. The fifth period starts at $Rb$ (Z = 37), where the $4d$ orbital first receives electrons. **Electron configuration pattern:** - Fourth period fills: $4s$, then $3d$, then $4p$ orbitals - $4d$ orbital is empty throughout the entire fourth period **Conclusion:** **Zero elements** in the fourth period have 4d electrons. Since the correct answer is listed as **C**, option C must represent **0** (or "none").