STD 12 - 4. d and f- block elements — NEET STD 11 Science — Question

All other elements are $d-block$ elements therefore has valance electron in $3 d$ subshell.

Electronic configuration of $Cr ( I )$ is $1 s^2 2 s^2 2 p^6 3 s^2 3 p^6 3 d^5$.

Electronic configuration of $F (III)$ is $1 s^2 2 s^2 2 p^6 3 s^2 3 p^6 3 d^5$

Electronic configuration of $Mn (II)$ is $1 s^2 2 s^2 2 p^6 3 s^2 3 p^6 3 d^5$.

So, all these have valence electrons in $3 d$ - subshell.