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

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

borax dissolves in water to give alkaline solution of sodium hydroxide and orthoboric acid .since orthoboric acid is weak monobasic acid resulting solution is alkaline.

${\mathrm{Na}}_2{\mathrm{B}}_4{\mathrm{O}}_7 + 7{\mathrm{H}}_2\mathrm{O} \to 2\mathrm{NaOH} + 4{\mathrm{H}}_3{\mathrm{BO}}_3(\mathrm{orthoboric} \mathrm{acid} )$