Acid, Base and Salts MCQ question and answer with solution | Chemistry Gk MCQs

* Acidity often comes from a molecule's ability to donate a proton (H+) or accept electrons.
* In the context of these chlorides, we need to consider how they react with water (hydrolyze). Some will form acidic solutions because of this reaction.
Now let's look at the options:
* PCl₄: This compound is unstable and doesn't exist under normal conditions. But theoretically, if it reacted with water, it could potentially form phosphorus-containing acids.
* SbCl₄: Antimony tetrachloride can hydrolyze to form acidic solutions containing antimony oxychlorides and hydrochloric acid.
* CCl₄: Carbon tetrachloride (CCl₄) is not acidic. It doesn't react with water easily. The carbon-chlorine bond is relatively strong, and there isn't a good mechanism for it to hydrolyze and release H+ ions.
* PCl₂: This compound is unstable and doesn't exist under normal conditions. Similar to PCl4 it is capable of forming phosphorus-containing acids.
Therefore:
The answer is CCl₄ because it doesn't readily hydrolyze to produce acidic species in water.

Let's understand what basicity of an acid means first.
The basicity of an acid is simply the number of ionizable hydrogen atoms (H⁺) that one molecule of the acid can donate when it dissolves in water.
Think of it like this: how many "acidic" hydrogens can it give away?

If an acid has basicity one, it means it can donate only one H⁺ ion. We call such an acid a monoprotic acid.
Let's look at the options:

Option A: Phosphoric acid (H₃PO₄)
This acid has three (3) ionizable hydrogen atoms.
So, it can donate 3 H⁺ ions.
Its basicity is three.
Therefore, this option is incorrect.

Option B: Sodium dihydrogen phosphate (NaH₂PO₄)
This is a salt. However, the H₂PO₄⁻ ion in this salt still has two (2) hydrogen atoms that can be donated as H⁺ ions.
So, if it acts as an acid, its basicity would be two.
Therefore, this option is incorrect.

Option C: Disodium hydrogen phosphate (Na₂HPO₄)
This is also a salt. The HPO₄²⁻ ion in this salt has one (1) hydrogen atom that can be donated as an H⁺ ion.
So, if it acts as an acid, its basicity is one.
This matches what the question is asking for!
Therefore, this option is correct.

Option D: Sodium phosphate (Na₃PO₄)
This is a salt. The PO₄³⁻ ion in this salt has no (0) hydrogen atoms to donate as H⁺ ions.
In fact, it's a basic salt.
So, its basicity is zero.
Therefore, this option is incorrect.

So, the correct answer is Disodium hydrogen phosphate (Na₂HPO₄) because it can donate only one H⁺ ion.