Identify a molecule with an incomplete octet from the following.

The number of $\sigma$ and $\pi$ bonds in $O_3$ molecule is:

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

Which of the following fluoro compounds acts as a Lewis base?

Identify the correct statements from the following.
$(I)$ $SnCl_2$ is ionic,but $SnCl_4$ is covalent in nature.
$(II)$ All linear diatomic molecules have zero dipole moment.
$(III)$ Both $NO$ and $O_2$ are paramagnetic.

Which of the following is not used as a Lewis acid?