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What are strong acids and weak acids?
a.) An acid which dissociates completely or almost completely in water is called a strong acid whereas an acid which only partially does so is referred to as a weak acid.
b.) An acid which dissociates completely is called a strong acid whereas an acid which dissociates almost completely in water is referred to as a weak acid.
c.) An acid which does not dissociate completely in water is referred to as a strong acid whereas an acid which dissociates almost completely in water is called a weak acid.
d.) An acid that dissociates only partially in water is referred to as a strong acid whereas an acid that does not completely dissociate in water is called a weak acid.

Answer Verified Verified
Hint: Examples of strong acids include: HCl, ${{H}_{2}}S{{O}_{4}}$ etc.
Examples of weak acids include: HCOOH, $C{{H}_{3}}COOH$ etc.
Think of what distinct chemical property differentiates these two classes of acids.

Complete step-by-step answer:
Let us discuss both these terms: strong acids and weak acids; one at a time.
A strong acid is one which is virtually 100% ionised in solution and splits into aqueous versions of its constituent cation and anion.
Some common strong acids include sulphuric acid, hydrochloric acid and nitric acid.

Here is the equation for the ionisation of Hydrochloric Acid (HCl) written in a simplified form:
$HC{{l}_{(aq)}}\to {{H}^{+}}_{(aq)}+C{{l}^{-}}_{(aq)}$

This shows the hydrogen chloride dissolved in the water splitting to give hydrogen ions in solution and chloride ions in solution.
Now let us discuss what a weak acid really is.
By contrast, a weak acid is one which doesn't ionise fully when it is dissolved in water.
Ethanoic acid is a typical weak acid. It reacts with water to produce hydronium ions and ethanoate ions, but the back reaction is more successful than the forward one. The ions react very easily to reform the acid and the water.
$C{{H}_{3}}COOH+{{H}_{2}}O \longrightarrow C{{H}_{3}}CO{{O}^{-}}+H_3{{O}^{+}}$
At any one time, only about 1% of the ethanoic acid molecules have converted into ions. The rest remain as simple ethanoic acid molecules.
Therefore, from the above analysis and explanation we can conclude that the answer to this question is a).

NOTE: Please be as clear as possible with the concept of ionisation in water of different compounds as the knowledge of this concept is essential for you to be able to solve this question easily.
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