The electronic configurations of three elements X, Y and Z are $2,8$; $2,8,7$; and $2,8,2$ respectively. Which of the following is correct?

The correct option is D $Y$ is a non-metal and $Z$ is a metal
$X=2,8=10$: It is the electronic configuration of neon.
$Y=2,8,7=17$: It is the configuration of the halogen family of chlorine atom which is non-metal
$Z=2,8,2=12$: It is the configuration of alkaline earth metals of magnesium atom which is metal.

Therefore, X is a noble gas, Y is a non-metal, and Z is a metal.

Option D is correct.