JEE Main · 2021 · 24 Feb 2021 · Shift 1 · s-Block Elements

Amphoteric compounds are those that can react with both acids and bases.

Analysis of each compound:

(A) BeO (Beryllium oxide): Amphoteric

• Reacts with acids: $\mathrm{BeO}+2\mathrm{HCl}\to {\mathrm{BeCl}}_2+{\mathrm{H}}_2\mathrm{O}$
• Reacts with bases: $\mathrm{BeO}+2\mathrm{NaOH}+{\mathrm{H}}_2\mathrm{O}\to {\mathrm{Na}}_2[\mathrm{Be}(\mathrm{OH}{)}_4]$

(B) BaO (Barium oxide): Basic (not amphoteric)

• Barium is a Group 2 element with large size; its oxide is strongly basic.

**(C) $\mathrm{Be}(\mathrm{OH}{)}_2$ (Beryllium hydroxide):** Amphoteric

• Reacts with acids: $\mathrm{Be}(\mathrm{OH}{)}_2+2\mathrm{HCl}\to {\mathrm{BeCl}}_2+2{\mathrm{H}}_2\mathrm{O}$
• Reacts with bases: $\mathrm{Be}(\mathrm{OH}{)}_2+2\mathrm{NaOH}\to {\mathrm{Na}}_2[\mathrm{Be}(\mathrm{OH}{)}_4]$

**(D) $\mathrm{Sr}(\mathrm{OH}{)}_2$ (Strontium hydroxide):** Basic (not amphoteric)

• Strontium is a Group 2 element; its hydroxide is strongly basic.

Beryllium, being small in size and having high charge density, shows anomalous behavior and forms amphoteric oxides and hydroxides.

Number of amphoteric compounds = 2 (BeO and Be(OH)₂)

Answer: 2