An amphoteric hydroxide is a substance that can act as both an acid and a base. This means it can react with both acids and bases. For hydroxides, this behavior is often observed in elements that lie on the diagonal line of the periodic table, such as beryllium (Be), aluminum (Al), zinc (Zn), etc.

Let's analyze the given options:

• $\mathrm{Sr}\left(\mathrm{OH}\right)2$: Strontium hydroxide is a strong base and not amphoteric.

• $\mathrm{Mg}\left(\mathrm{OH}\right)2$: Magnesium hydroxide is a weak base and not amphoteric.

• $\mathrm{Ca}\left(\mathrm{OH}\right)2$: Calcium hydroxide is a strong base and not amphoteric.

• $\mathrm{Be}\left(\mathrm{OH}\right)2$: Beryllium hydroxide is amphoteric. It reacts with acids and bases:

  With acid: $\mathrm{Be}\left(\mathrm{OH}\right)2+2\mathrm{HCl}\to \mathrm{BeCl}2+2H2O$

  With base: $\mathrm{Be}\left(\mathrm{OH}\right)2+2\mathrm{NaOH}\to \mathrm{Na}2\left[\mathrm{Be}\right(\mathrm{OH}\left)4\right]$

Thus, the correct answer is Be(OH)₂.

Related Topics

Amphoteric Behavior: Some hydroxides and oxides can act as both acids and bases. This is common for elements that are metalloids or near the metalloid line in the periodic table.

Periodic Trends: Amphoterism is often observed in elements like Be, Al, Zn, Sn, Pb due to their intermediate electronegativity and size, which allows them to lose or gain protons under different conditions.

Key Formulae

Reactions showing amphoteric nature:

Acidic reaction: $M\left(\mathrm{OH}\right)n+nH+\to Mn++nH2O$

Basic reaction: $M\left(\mathrm{OH}\right)n+n\mathrm{OH}-\to \left[M\right(\mathrm{OH})n+m]m-$