Equimolar solutions of the following compounds are prepared...

Metal halide on hydrolysis with water form corresponding hydroxides. The basic strength of hydroxide increases as we move down in a group. This is because of the increase in size which results in decrease of ionization energy which weakens the strength of $\mathrm{M}-\mathrm{O}$ bonds in MOH and thus increases the basic strength. $$\begin{aligned}& \mathrm{Be}(\mathrm{OH})_2 \quad \mathrm{Mg}(\mathrm{OH})_2 \\ & \text{ Amphoteric Weak base }\\ & \mathrm{Ca}(\mathrm{OH})_2 \mathrm{Sr}(\mathrm{OH})_2 \mathrm{Ba}(\mathrm{OH})_2 \\ & \end{aligned}$$Hence, $\mathrm{Be}(\mathrm{OH})_2$ will have lowest $\mathrm{pH}.