The empirical formula of permutit or zeolite used in ion-exchange method is

• A

  ${\mathrm{Na}}_{\mathrm{2}}{\mathrm{Al}}_{\mathrm{2}}{\mathrm{Si}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{8}}\cdot {\mathrm{xH}}_{\mathrm{2}}\mathrm{O}$

• B

  ${\mathrm{NaAlO}}_4·{\mathrm{xH}}_2\mathrm{O}$

• C

  ${\text{Na Al Si O}}_{\text{4}}\cdot {\mathrm{xH}}_2\mathrm{O}$

• D

  ${\text{Na Fe Si O}}_{\text{4}}\cdot {\mathrm{xH}}_2\mathrm{O}$