Q.Po (belongs to period 6 and group 16)

Step 1. Note the period and group. Po is in period 6 (outermost shell n=6) and group 16 (general outer configuration $ns^2np^4$).

Step 2. Build up through period 6. Period 6 fills in the order $6s < 4f < 5d < 6p$ (Problem 7.2). Starting from $[Xe]$: $6s^2$ (Cs, Ba) → $4f^{1-14}$ (the lanthanoid series) → $5d^{1-10}$ (the d-block row of period 6) → $6p^{1-6}$ (the p-block row of period 6). Po is the fourth p-block element of period 6, so its 6p subshell holds 4 electrons.

Step 3. Write the full configuration. $Po: [Xe]6s^24f^{14}5d^{10}6p^4$. …

Building the configuration via period-6 Aufbau order (6s<4f<5d<6p) and confirming …

• Omitting the 4f¹⁴ lanthanoid-series block, which must be filled before 5d in period 6. …