Which of the following species among $BF_3, SnCl_2, SnCl_4$ act as Lewis acids?

The oxidation state $(n)$,coordination number $(CN)$ of $Al$,and the number of valence electrons around $Al$ $(N)$ in $Al_2Cl_6$ are respectively:

Which of the following statements is true with respect to $H_2O$,$NH_3$ and $CH_4$?
$A.$ The central atoms of all the molecules are $sp^3$ hybridized.
$B.$ The $H-O-H$,$H-N-H$ and $H-C-H$ angles in the above molecules are $104.5^{\circ}$,$107.5^{\circ}$ and $109.5^{\circ}$ respectively.
$C.$ The increasing order of dipole moment is $CH_4 < NH_3 < H_2O$.
$D.$ Both $H_2O$ and $NH_3$ are Lewis acids and $CH_4$ is a Lewis base.
$E.$ $A$ solution of $NH_3$ in $H_2O$ is basic. In this solution,$NH_3$ and $H_2O$ act as a Lowry-Bronsted base and acid respectively.
Choose the correct answer from the options given below:

What is the formal charge on a hydrogen atom in a water molecule?

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

Which of the following compounds does not exist?