Which of the following has a three-electron bond in its structure?

Which of the following is diamagnetic?

If an extra electron is added to the hypothetical molecule $C_{2}$,this extra electron will occupy the molecular orbital.

Identify the correct increasing order of energies of molecular orbitals for the $F_2$ molecule.

The bond order in $O_2^{2-}$ is

Consider the following changes $I$ and $II$ as shown in the figure. The correct statements about these changes $(I)$ and $(II)$ in accordance with $MO$ theory are:
$A$) In $(I)$ bond order increases by $0.5$ from the existing value.
$B$) In $(II)$ bond order decreases by $0.5$ from the existing value.
$C$) In both $(I)$ and $(II)$ magnetic property is changed.
$D$) In both $(I)$ and $(II)$ magnetic property is not changed.