Select optically active complex(es):

Note: Solution corrected from that of book.

A complex of $\left[\mathrm{Pt}(\mathrm{L}{)}_{\mathrm{x}}\right]\left[\mathrm{Pt}(\mathrm{L}\text{'}{)}_{\mathrm{y}}\right]$ is prepared by reaction of platinum ions ${\mathrm{NH}}_3\left(\mathrm{L}\text{ or }{\mathrm{L}}^{\text{'}}\right)$ and ${\mathrm{C}}_2{\mathrm{O}}_4^{2-}\left(\mathrm{L}\text{ or }{\mathrm{L}}^{\text{'}}\right)$. Which of the following statements must be true for the complex?