Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R.
Assertion A : Order of acidic nature of the following compounds is A > B > C.

Reason R: Fluoro is a stronger electron withdrawing group than Chloro group.
In the light of the above statements, choose the correct answer from the options given below :

The three compounds are haloacetic acids: $$A = FCH_2COOH$$, $$B = ClCH_2COOH$$ and $$C = BrCH_2COOH$$.

Step 1 : Why the acidity order is $$A \gt B \gt C$$
When an acid $$HA$$ loses $$H^+$$ it forms its conjugate base $$A^-$$. The stronger the electron-withdrawing (-I) effect of the substituent, the better the negative charge on $$A^-$$ is delocalised and the more stable the anion becomes. Fluorine is the most electronegative of the three halogens followed by chlorine and then bromine. Hence the -I effect decreases in the order
$$F \gt Cl \gt Br$$.
Therefore the stability of the corresponding carboxylate anions and hence the acid strength follow the same sequence:
$$FCH_2COOH \; (A) \gt ClCH_2COOH \; (B) \gt BrCH_2COOH \; (C).$$
Thus Assertion A is correct.

Step 2 : Truth value of Reason R
Reason R states that “Fluoro is a stronger electron-withdrawing group than Chloro.” This statement is factually correct because the electronegativity of fluorine (4.0) is higher than that of chlorine (3.0). So Reason R itself is a true statement.

Step 3 : Does Reason R explain Assertion A?
To explain the complete order $$A \gt B \gt C$$ one must compare the -I effects of all three halogens $$F, Cl$$ and $$Br$$. Reason R compares only fluorine with chlorine and says nothing about bromine. Therefore, although R is correct, it is not a sufficient explanation for the full order stated in Assertion A.

Hence, both Assertion A and Reason R are true, but R is NOT the correct (complete) explanation of A.

Option D which is: Both A and R are correct but R is NOT the correct explanation of A.