Which of the following is not a Lewis acid?

The correct statements from the following are:
$a$) The total number of sigma bonds present in benzene is $12$
$b$) $LiF$ is more covalent than $KF$
$c$) $SnCl_2$ is more covalent than $SnCl_4$

Amongst the following,the total number of species $NOT$ having $8$ electrons around the central atom in its outermost shell is $NH_3$,$AlCl_3$,$BeCl_2$,$CCl_4$,$PCl_5$:

Calculate $x + y + z$ for $H_3PO_3$ acid,where $x$ is the number of lone pairs,$y$ is the number of $\sigma$ bonds,and $z$ is the number of $\pi$ bonds.

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

Blue vitriol contains which of the following types of bonds?