Borax dissolves in water to give alkaline solution. The missing chemical in the following equation is

${\mathrm{Na}}_2{\mathrm{B}}_4{\mathrm{O}}_7+7{\mathrm{H}}_2\mathrm{O}\stackrel{ }{\to }2\mathrm{NaOH}+.......$

• A

  ${\text{4H}}_{\text{3}}{\text{BO}}_4$

• B

  ${\text{4H}}_{\text{3}}{\text{BO}}_3$

• C

  ${\text{4H}}_{\text{3}}{\text{BO}}_2$

• D

  ${\text{4H}}_{\text{2}}{\text{BO}}_3$