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Question: Which of the following is only acidic in nature? (A) \(Be{{(OH)}_{2}}\) (B) \(Mg{{(OH)}_{2}}\) ...

Which of the following is only acidic in nature?
(A) Be(OH)2Be{{(OH)}_{2}}
(B) Mg(OH)2Mg{{(OH)}_{2}}
(C) B(OH)3B{{(OH)}_{3}}
(D) Al(OH)3Al{{(OH)}_{3}}

Explanation

Solution

Given options are all hydroxides. In order to get the answer of the given question, try to find out which option is indicated as metallic hydroxide and which is non-metallic hydroxide one. Remember, metallic hydroxides are basic in nature while non-metallic hydroxides are acidic in nature.

Complete step by step solution:
Given that, we have to find out which option is only acidic in nature and the options for this question are all hydroxides.
So, hydroxide is a chemical compound containing one or more groups consisting of one atom which is bound together by oxygen and hydrogen and acts as the negative charged −OH−-O{{H}^{-}} ion.
So, a compound is said to be acidic or basic depending upon what type of ion it releases when it is treated with an aqueous solution. If hydrogen ions (H+{{H}^{+}}) are released in its aqueous solution, then the compound is said to be acidic while it is said to be basic, when it releases hydroxyl ions (OH−O{{H}^{-}}).
Well, not all hydroxides behave as basic or acidic. Some of the hydroxyl-containing compounds behave as acidic while some used to behave as basic. There are some hydroxyl-containing compounds, which behave as amphoteric i.e. they have both the acidic and basic characteristics.
Generally, non-metallic hydroxides tend to be acidic in nature because the oxygen atoms polarize electron density towards themselves and weaken the O−HO-H bond and the negative charge is distributed to the other oxygen atoms, thus reducing the charge density and making it acidic in nature.
Metal hydroxides such as magnesium, calcium, aluminium possess a metal centre that is by no means electronegative and thus does not weaken the O−HO-H bond and hence release hydrogen ions and make it acidic in nature.
So, here Be(OH)2Be{{(OH)}_{2}}, Mg(OH)2Mg{{(OH)}_{2}} and Al(OH)3Al{{(OH)}_{3}}, all have a metal centre. Thus, they are basic in nature. Al(OH)3Al{{(OH)}_{3}} and Be(OH)2Be{{(OH)}_{2}}also acts as acidic in nature, thus making them amphoteric in nature i.e. both acidic and basic.
And the remaining, B(OH)3B{{(OH)}_{3}} has a non-metallic centre and it does not form a stable cation, thus it is acidic in nature.
Therefore, the only acidic compound is B(OH)3B{{(OH)}_{3}}.

Hence, the correct option is (C).

Note: Boron is the only element in the thirteenth of the periodic table which is non-metallic. Metal hydroxides should form a stable cation or anion but boron does not form a stable cation. This is the reason why metals form basic hydroxides while boron forms a weak acid called boric acid.