Which method is used to purify liquids having very high boiling points and liquids which decompose at or below their boiling point?

What are $X, Y, Z$ in the following reaction sequence?

But-2-ene $\xrightarrow{X}$ Ethanoic acid $\xrightarrow{Y}$ Ethanoyl chloride $\xrightarrow[\text { Anhy. } \mathrm{AlCl}_3]{\text { Benzene }} Z$

An element (atomic weight $=250 \mathrm{u}$ ) crystallises in a simple cubic lattice. If the density of the unit cell is $7.2 \mathrm{~g} \mathrm{~cm}^{-3}$. What is the radius (in $\mathop {\rm{A}}\limits^{\rm{o}}$ ) of the atom of the element?

$$ \left(N_A=6.02 \times 10^{23} \mathrm{~mol}^{-1}\right) $$

1.95 g of non-volatile and non-electrolyte solute dissolved in 100 g of benzene lowered the freezing point of it by 0.64 K .

The molar mass of the solute (in $\mathrm{g} \mathrm{mol}^{-1}$ )

$$ \left(K_f\left(\mathrm{C}_6 \mathrm{H}_6\right)=5.12 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1}\right) $$