In $Sr$ $(Z=38)$, the number of electrons with $l=0$ is $x$, and the number of electrons with $l=2$ is $y$. The value of $(x-y)$ is equal to:
($l=$ Azimuthal quantum number)

• A
  $0$
• B
  $8$
• C
  $-2$
• D
  $2$