The total number of lone pairs of electrons in melamine is

Which of the following statement$(s)$ is/are correct?

In the solid state,$PCl_5$ exists as which of the following?

Match the items in List-$I$ with the appropriate examples in List-$II$.

List-$I$	List-$II$
$(1)$ Hydrogen bond	$(A)$ ${\rm{C}}$
$(2)$ Resonance	$(B)$ ${\rm{LiF}}$
$(3)$ Ionic solid	$(C)$ ${\rm{H}}_2$
$(4)$ Covalent solid	$(D)$ ${\rm{HF}}$
	$(E)$ ${\rm{O}}_3$

Compound $X$ is the anhydride of sulphuric acid. The number of $\sigma$-bonds and the number of $\pi$-bonds present in $X$ are,respectively:

Which of the following statements is incorrect?
$(i)$ $NaCl$,being an ionic compound,is a good conductor of electricity in the solid state.
$(ii)$ In canonical structures,there is no difference in the arrangement of atoms.
$(iii)$ Hybrid orbitals form stronger bonds than pure orbitals.
$(iv)$ $VSEPR$ theory can explain the square planar geometry of $XeF_4$.