In allene structure three carbon atoms are joined by :

Which of the following molecules is nonpolar?

$\left(\mathrm{i}\right)$ ${\mathrm{PbCl}}_4$
$\left(\mathrm{ii}\right)$ ${\mathrm{BF}}_3$
$\left(\mathrm{iii}\right)$ ${\mathrm{SnCl}}_2$
$\left(\mathrm{iv}\right)$ ${\mathrm{CS}}_2$

One of the resonating structure of ${\mathrm{SO}}_4^{-2}$ is

Which set of formal charge on oxygen and bond order is correct