Which of the following triatomic molecules does not exist?

Assertion : Bond angle of $H_2S$ is smaller than $H_2O$.
Reason : Electronegativity of the central atom increases,bond angle decreases.

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

Who first provided an explanation for the formation of chemical bonds in terms of electrons?

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 $SnCl_4$

Select the correct statement.