Consider the following specific elements from the 2nd and 3rd periods: and . Based on periodic trend — Periodic Table and Periodicity Chemistry Question

💡 Solution & Explanation

Beryllium has a stable fully-filled $2s^2$ configuration. Comparing values: $Li < Be$. Due to penetration effect, $B < Be$. Going down the group, $Mg < Be$. $Na$ is an alkali metal below $Li$, so $Na < Li < Be$. Elements to the right ($C, N, O$) have higher $Z_{eff}$ and thus higher IE than $Be$. The elements with lower $IE_1$ than $Be$ are $Li, B, Na,$ and $Mg$. Total = 4.