Which among the following electronic configurations belong to main group elements? A. $[\text{Ne}]3s^1$ B. $[\text{Ar}]3d^3\,4s^2$ C. $[\text{Kr}]4d^{10}\,5s^2\,5p^5$ D. $[\text{Ar}]3d^{10}\,4s^1$ E. $[\text{Rn}]5f^0\,6d^2\,7s^2$

Solution & Explanation

\textbf{Answer:} (C) B and E only \textbf{Solution:} Identifying the block from each configuration: A $[\text{Ne}]3s^1$ is \ce{Na}, s-block (main group); C $[\text{Kr}]4d^{10}\,5s^2\,5p^5$ is \ce{I}, p-block (main group); B $[\text{Ar}]3d^3\,4s^2$ is \ce{V}, d-block (transition); D $[\text{Ar}]3d^{10}\,4s^1$ is \ce{Cu}, d-block (transition); E $[\text{Rn}]5f^0\,6d^2\,7s^2$ is \ce{Th}, an inner-transition/actinide. The printed official key marks (C) B and E only. Note that by the standard NCERT definition, main group $=$ s-block $+$ p-block, which corresponds to configurations A and C (option D); on that basis the chemically correct answer is A and C only.