Four diatomic species are listed below in different sequences. Which of these presents the correct order of their increasing bond order ?

$\begin {array} {1 1} (1)\;He_2^+<O_2^-<NO<C_2^{2-} & \quad (2)\;O_2^-<NO<C_2^{2-}<He_2^+ \\ (3)\;NO<C_2^{2-}<O_2^-<He_2^+ & \quad (4)\;C_2^{2-}<He_2^+<NO<O_2^- \end {array}$