$\alpha$ - butylene when subjected to hydroboration oxidation reaction, yields

Calculate van't Hoff-factor for 0.2 m aqueous solution of KCl which freezes at $-0.680^{\circ} \mathrm{C}$. $\left(K_f=1.86 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1}\right)$

Which among the following sets of compounds is used as raw material for the preparation of sodium carbonate by Solvay process?

What is the $\mathrm{H}-\mathrm{S}-\mathrm{H}$ bond angle in $\mathrm{H}_2 \mathrm{~S}$ ?