How many $S-S$ bonds are present in the cyclic trimer of sulfur trioxide,$(SO_3)_3$?

The correct order for $O-O$ bond length in the given substances is:
$I.$ $H_2O_2$
$II.$ $O_2$
$III.$ $O_3$

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 $XeF_4$.

Assertion: $H_2O$ and $XeF_4$ both have a plane of symmetry.
Reason: $H_2O$ is a polar molecule,whereas $XeF_4$ is a non-polar molecule.

The bonds present in $N_2O_{5(s)}$ is/are:
$I$. Ionic
$II$. Covalent
$III$. Coordinate

The sum of $\pi$-bonds present in peroxodisulphuric acid and pyrosulphuric acid is: