Which one of the following should be most stable?

Consider the given figure showing the formation of $H^{+}_2$ ion depending on internuclear distance versus potential energy of the system.
Which is the correct statement?

In $O_2^-$,$O_2$,and $O_2^{2-}$ molecular species,the total number of antibonding electrons respectively are

Which of the following molecular orbitals has two nodal planes?

Which one of the following has no unpaired electrons?

Explain the conduction of electricity in metals.