Consider the following electronic configurations of neutral atoms:...

The block of an element is determined by the subshell in which the last electron enters.

A. $[\mathrm{Ne}] 3s^2 3p^4$: The last electron enters the $3p$ subshell, so it is a p-block element (Group 16).

B. $[\mathrm{Ar}] 3d^6 4s^2$: The last electron enters the $3d$ subshell, so it is a d-block element (Group 8).

C. $[\mathrm{Kr}] 4d^{10} 5s^2$: The last electron enters the $4d$ subshell, so it is a d-block element (Group 12).

D. $[\mathrm{Xe}] 4f^{14} 5d^{10} 6s^2 6p^2$: The last electron enters the $6p$ subshell, so it is a p-block element (Group 14).

E. $[\mathrm{Ar}] 3d^5 4s^1$: The last electron enters the $3d$ subshell, so it is a d-block element (Group 6).

Therefore, configurations B, C, and E represent d-block elements.