$O_2^{2-}$ is the symbol of which ion?

In which species,$X-O$ bond order is $1.5$ and contains $p\pi - d\pi$ bond$(s)$?

Identify the molecule / ion in which the ratio of $\sigma$ to $\pi$ bonds is $3: 2$.

Which of the following compounds $CANNOT$ act as a Lewis base?

In the trimer form of sulphur trioxide $(S_3O_9)$,each sulphur atom is bonded with:

Which of the following have $X-O-X$ linkage? (where $X$ is the central atom):
$(i) \ Cr_2O_7^{2-}$
$(ii) \ S_2O_3^{2-}$
$(iii) \ \text{Pyrosilicate}$
$(iv) \ \text{Hyponitrous acid}$