Question

Beryllium forms a diagonal relationship with aluminium. Which one of the following similarities is incorrect?
(A) $\text{B}{{\text{e}}_{\text{2}}}\text{C}$ like $\text{A}{{\text{l}}_{\text{4}}}{{\text{C}}_{\text{3}}}$ yields methane on hydrolysis.
(B) $\text{Be}$ like $\text{Al}$ is rendered passive by $\text{HN}{{\text{O}}_{\text{3}}}$ .
(C) $\text{Be}{{\left( \text{OH} \right)}_{\text{2}}}$ like $\text{Al}{{\left( \text{OH} \right)}_{3}}$ is basic.
(D) $\text{Be}$ forms beryllates while $\text{Al}$ forms aluminates.

Answer 1

The diagonal relationship is shared between those elements in the periodic table that are diagonally opposite to each other and they show certain resemblances among each other’s properties. Such as, lithium and magnesium and beryllium and aluminium. They also share the type of compounds they can form.

Complete step by step solution
Beryllium carbide reacts with water or gets hydrolysed by water to form methane gas and beryllium oxide. Aluminium carbide also reacts with water to form methane gas and aluminium hydroxide is formed along with that. Hence, $\text{B}{{\text{e}}_{\text{2}}}\text{C}$ like $\text{A}{{\text{l}}_{\text{4}}}{{\text{C}}_{\text{3}}}$ yields methane on hydrolysis is correct.
When beryllium reacts with nitric acid then a layer of beryllium oxide is formed as a coating on the surface of beryllium just like a surface of aluminium oxide is formed when aluminium reacts with nitric acid, thus rendering it basic. Hence, $\text{Be}$ like $\text{Al}$ is rendered passive by $\text{HN}{{\text{O}}_{\text{3}}}$ is also true.
Beryllium hydroxide is an amphoteric compound that dissolves in both acids as well as alkalis while aluminium hydroxide is also amphoteric in nature, hence, $\text{Be}{{\left( \text{OH} \right)}_{\text{2}}}$ like $\text{Al}{{\left( \text{OH} \right)}_{3}}$ is basic is incorrect.
$\text{Be}$ forms beryllates while $\text{Al}$ forms aluminates in which the formula of the beryllate ion is $\text{Be}{{\text{O}}_{\text{2}}}^{\text{2-}}$ formed when beryllium is dissolve in a basic solution and aluminium forms a similar type of anion $\text{Al}{{\text{O}}_{\text{2}}}^{\text{-}}$ . Hence this is correct.
So, the option that is incorrect is C.

Note
Beside those points are that mentioned above there are other similarities between beryllium and aluminium as well. Both of them form the covalent halides due to the highly polarising nature of the beryllium and the aluminium ion.