Which of the following are isoelectronic species?
$I. CH_{3}^{+}$,$II. H_{3}O^{+}$,$III. NH_{3}$,$IV. CH_{3}^{-}$

In which of the following molecules,all atoms are coplanar?

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

Which of the following does not have the correct order of the given property?

Which of the following is not a Lewis acid?

Which of the following contains both covalent and ionic bonds?