Which of the following substance has zero value of $ \Delta G_f^{\circ} $?

Question

$\begin {array} {1 1} (A)\;Br_2 (aq) & \quad (B)\;Br_2 (l) \\ (C)\;Br_2 (g) & \quad (D)\;Br_2 (s) \end {array}$