What is the number of tetrahedral voids present in $0.5$ mole of compound forming hcp structure?

Which among the following pairs of solutions is isotonic in nature?

A solution of non volatile solute has boiling point elevation $0.70$ K if $K_b$ for the solvent is $2.44\ \text{K kg mol}^{-1}$. What is the molality of the solution?

van't Hoff factor for $\text{BaCl}_2$ is $2.47$, calculate the percentage dissociation of in its aqueous solution.