Zeolite is a silicate of two metal ions $X$ and $Y$. $X$ and $Y$ are respectively

• A
  $Ca^{2+}, Na^{+}$
• B
  $Mg^{2+}, Na^{+}$
• C
  $Na^{+}, Al^{3+}$
• D
  $Ca^{2+}, Mg^{2+}$