Question

$Cr$ has electronic configuration as:

• A. $\left[Ne\right]3s^2,3p^6,3d^4,4s^1$
• B. $\left[Ne\right]3s^2,3p^6,3d^5,4s^1$
• C. $\left[Ne\right]3s^2,3p^6,3d^6$
• D. none of the above

Answer 1

The correct option is B $\left[Ne\right]3s^2,3p^6,3d^5,4s^1$

Cr has atomic number of $24$. It;s electronic configuration hence is expected to be $\left[Ar\right]3d^{4}4s^2$ but it is observed to be $\left[Ar\right]3d^{5}4s^1$. This is because $3d^5$ is half filled and thus provides more stability. Thus configuration of Cr is $\left[Ar\right]3d^{5}4s^1$ or $\left[Ne\right]3s^{2}3p^{6}3d^{5}4s^1$