Cr_2O_7^2- dissolves in aqueous NaOH to give:

The correct answer is Option (3) → ${CrO_4}^{2-}$

The chromates and dichromates are interconvertible in aqueous solution depending upon the pH of the solution.

Dichromate ion $(\text{Cr}_2\text{O}_7^{2-})$ produces chromate ion $(\text{CrO}_4^{2-})$ and a water molecule in basic solutions like NaOH.

${2 CrO_4^{2-} + 2 H^+→Cr_2O_7^{2-} + H_2O}$

${Cr_2O_7^{2-} + 2 OH^-  →2 CrO_4^{2-} + H_2O}$