Which of the following is a non-electrolyte?

The freezing point depression constant for water is $1.86 \, ^\circ C \, m^{-1}$. If $5.00 \, g$ of $Na_2SO_4$ is dissolved in $45.0 \, g$ of $H_2O$,the freezing point is changed by $3.82 \, ^\circ C$. Calculate the van't Hoff factor $(i)$ for $Na_2SO_4$.

Which of the following is a non-electrolyte?

$0.004 \ M$ $Na_2SO_4$ solution is isotonic with $0.01 \ M$ glucose solution,then the degree of dissociation of $Na_2SO_4$ is ........... $\%$.

The van't Hoff factor for $Ca(NO_3)_2$ is ...... .

$A^{2+}$,$B^{2+}$ and $C^{-}$ form an ionic complex like $A_{x-2}[B(C)_x]_2$. If the complex is $75 \%$ dissociated in a solvent with $i=4$,the coordination number of $B$ is: