Amphoteric hydroxides react with both alkalies with acids. Which of the following Group 2 metal hydroxides is soluble in sodium hydroxide?

1. $\mathrm{Be}{\left(\mathrm{OH}\right)}_{2}$

2. $\mathrm{Mg}{\left(\mathrm{OH}\right)}_{2}$

3. $\mathrm{Ca}{\left(\mathrm{OH}\right)}_{2}$

4. $\mathrm{Ba}{\left(\mathrm{OH}\right)}_{2}$

Hint: Beryllium oxide, and hydroxide are amphoteric in nature.

The solubility of hydroxides of alkaline earth metals increases from Be to Ba, in water. $\mathrm{Be}{\left(\mathrm{OH}\right)}_{2}$ and $\mathrm{Mg}{\left(\mathrm{OH}\right)}_{2}$ are almost insoluble.
Due to high hydration enthalpy and high lattice energy $\mathrm{Be}{\left(\mathrm{OH}\right)}_{2}$ is not soluble in water. $\mathrm{Be}{\left(\mathrm{OH}\right)}_{2}$ is an amphoteric hydroxide. With acids, $\mathrm{Be}{\left(\mathrm{OH}\right)}_{2}$ is neutralized giving salts.
$\mathrm{Be}{\left(\mathrm{OH}\right)}_{2}+2\mathrm{HCl}\to {\mathrm{BeCl}}_{2}+2{\mathrm{H}}_{2}\mathrm{O}$
$\mathrm{Be}{\left(\mathrm{OH}\right)}_{2}$ reacts with NaOH also forming beryllate.
$\mathrm{Be}{\left(\mathrm{OH}\right)}_{2}+2\mathrm{NaOH}\to {\mathrm{Na}}_{2}{\mathrm{BeO}}_{2}+2{\mathrm{H}}_{2}\mathrm{O}$