Which of the following is not paramagnetic?

Which of the following statements is correct?

The paramagnetic nature of the oxygen molecule $(O_2)$ is best explained on the basis of:

Which of the following species,$O_2$,$O_2^+$,and $O_2^-$,has the lowest bond order?

The set of species having only fractional bond order values is

Fill in the blanks given below:
$(i)$ The Molecular Orbital Theory was proposed by .......... and .......... scientists.
$(ii)$ The addition of atomic orbitals results in the formation of ............ orbitals.
$(iii)$ The distribution of electrons in molecular orbitals is called .......... .
$(iv)$ The number of bonds between atoms joined by a covalent bond is called .......... .