Animated Solution for Chemistry - s and p-Block Elements: Number of amphoteric compounds among the following is ......... . (a) $\text{BeO}$ (b) $\text{BaO}$ (c) ${\text{Be(OH)}}_2$ (d) ${\text{Sr(OH)}}_2$

When we dive into the world of inorganic chemistry, we often classify compounds as either acidic or basic. But nature loves exceptions! An amphoteric compound is a chemical chameleon—it can act as both an acid and a base depending on the environment it finds itself in. In this problem, we are given four compounds: $\text{BeO}$, $\text{BaO}$, ${\text{Be(OH)}}_2$, and ${\text{Sr(OH)}}_2$, and we need to identify the amphoteric ones.

To solve this, we must look at the periodic table. All the elements given belong to Group 2, the alkaline earth metals. Normally, as we move down Group 2, the metallic character increases, and their oxides and hydroxides become increasingly basic.

However, Beryllium ($\text{Be}$), the very first element of the group, is a rebel. Because of its exceptionally small size and high charge density, it exhibits an anomalous behavior. It forms a diagonal relationship with Aluminum ($\text{Al}$) from Group 13. Just like Aluminum, Beryllium forms covalent compounds, and more importantly, its oxide and hydroxide are amphoteric!

Let's put our candidates to the test:

1. Beryllium Oxide ($\text{BeO}$) As we just established, $\text{BeO}$ is amphoteric. It reacts with strong acids like $\text{HCl}$ to form salts:

And it also reacts with strong bases like $\text{NaOH}$ to form a complex beryllate ion:

2. Barium Oxide ($\text{BaO}$) Barium is located far down in Group 2. Its large atomic radius makes it highly electropositive. Therefore, $\text{BaO}$ is strictly a basic oxide. It dissolves in water to give a strongly alkaline solution of Barium hydroxide.

3. Beryllium Hydroxide (${\text{Be(OH)}}_2$) Following the exact same logic as its oxide, Beryllium hydroxide is also amphoteric. It dissolves in both acids and alkalis.

4. Strontium Hydroxide (${\text{Sr(OH)}}_2$) Strontium is another heavy alkaline earth metal. Its hydroxide is a strong base and shows no acidic properties whatsoever.

Out of the four compounds provided, only $\text{BeO}$ and ${\text{Be(OH)}}_2$ possess the unique ability to react with both acids and bases. The other two are strictly basic.

Therefore, the total number of amphoteric compounds is exactly $2$. Always keep an eye out for Beryllium in s-block questions—it almost always brings a twist to the standard group trends!