Identify the INCORRECT order among the following periodic trends for the representative elements: — Periodic Table and Periodicity Chemistry Question

💡 Solution & Explanation

The effective nuclear charge ($Z_{eff}$) does not strictly decrease down the alkali metal group. Instead, it initially increases from $Li$ to $Na$ and then remains almost constant ($Li=1.30$, $Na \approx 2.20$, $K \approx 2.20$, $Rb \approx 2.20$). Shielding increases down the group, atomic size increases, and the given ionic radii order correctly follows the isoelectronic series trend (size $\propto 1/Z$).