${\mathrm{CrO}}_3$ dissolves in aqueous $\mathrm{NaOH}$ to give

 ${\mathrm{CrO}}_3$ dissolves in aqueous $\mathrm{NaOH}$ to give  ${\mathrm{Na}}_2{\mathrm{CrO}}_4$ compound or  ${\mathrm{CrO}}_4^{2-}\text{ ion. }$

${\mathrm{CrO}}_3+2\mathrm{NaOH}\to \underset{\text{ yellow solution }}{{\mathrm{Na}}_2{\mathrm{CrO}}_4}+{\mathrm{H}}_2\mathrm{O}$