VerifiedHint:The electron withdrawing groups present in a molecule tends to increase the acidic strength of that molecule while the electron donating groups present in a molecule tends to decrease the acidic strength of that molecule.
Complete step by step answer:
In chemistry, the term ‘electron withdrawing group’ refers to the type of atoms or groups which can attract or pull the electron density of the atoms in their neighborhood towards themselves by the inductive effect or resonance effect. Examples of electron withdrawing groups are ${\text{ - F, - Cl, - OR, - C}}{{\text{F}}_{\text{3}}}{\text{, - CN, - OCOR}}$ etc.
On the other hand, the term ‘electron donating group’ or ‘electron releasing group’ refers to the type of atoms or groups which can donate or release their electron densities to the atoms in their neighborhood. Examples of electron donating groups are ${\text{ - R, - N}}{{\text{H}}_{\text{2}}}{\text{, - N}}{{\text{R}}_{\text{2}}}$ etc.
Now, in the question we are given three carboxylic acids viz., acetic acid $\left( {{\text{C}}{{\text{H}}_{\text{3}}}{\text{COOH}}} \right)$ , 2-methoxyacetic acid $\left( {{\text{C}}{{\text{H}}_{\text{3}}}{\text{OC}}{{\text{H}}_{\text{2}}}{\text{COOH}}} \right)$ and trifluoroacetic acid $\left( {{\text{C}}{{\text{F}}_{\text{3}}}{\text{COOH}}} \right)$ and we need to find out the correct order of their acidic strengths.
We can see that both 2-methoxyacetic acid and trifluoroacetic acid contain the electron withdrawing groups – methoxy group and ${\text{ - C}}{{\text{F}}_{\text{3}}}$ respectively. So both of these groups will disperse the negative charge by resonance or inductive effect and stabilize the carboxylate anion. As a result, the acidity of these two acids will increase as compared to acetic acid which does not have any kind of electron withdrawing group attached. So they will have higher acidic strength than acetic acid or a < b and a < c.
But the ${\text{ - C}}{{\text{F}}_{\text{3}}}$ group has three fluorine atoms and since fluorine is the most electronegative element, the electron withdrawing power of ${\text{ - C}}{{\text{F}}_{\text{3}}}$ is higher than that of methoxy group. So the acidic strength of 2-methoxyacetic acid is less than that of trifluoroacetic acid or b < c.
Thus, the final order will be, a<b<c. So, option A is correct.
Note:More the electron withdrawing power of the electron withdrawing group, higher will be the acidic strength of the acid. Some other factors on which the acidic strength of carboxylic acids depends are the effect of nature of halogens, effect of the number of halogen atoms, effect of the position of the halogen atom and effect of the type of hybridization of carbon atom carrying the carboxyl group.
