Which of the following is a Lewis acid?

For the following species,determine whether the octet rule is obeyed or not obeyed. Provide the reason for each:
$(1) BeF_4^{2-}$
$(2) BF_3$
$(3) CO_2$
$(4) NO$
$(5) NH_3$

If two different non-axial $d-$orbitals having $xz$ nodal plane form $\pi-$bond by overlapping each other,then the internuclear axis will be:

In the $OF_2$ molecule,the number of bonding and lone pairs of electrons are,respectively,........

The total number of lone pairs of electrons on oxygen atoms of ozone $(O_3)$ is $...........$.

Which of the following species contains four lone pairs of electrons?