Assertion (A): The pK$_a$ of O$_2$N–CH$_2$–COOH is lower than that of CH$_3$–COOH.
Reason (R): The –NO$_2$ group shows an electron-withdrawing effect, which increases the acidic character of O$_2$N–CH$_2$–COOH.
Show Hint
Electron-withdrawing groups increase acidity by stabilizing the conjugate base, while electron-donating groups decrease acidity by destabilizing it.
Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of
the Assertion (A).
Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct
explanation of the Assertion (A).
Assertion (A) is true, but Reason (R) is false
Assertion (A) is false, but Reason (R) is true.
Show Solution
The Correct Option isA
Solution and Explanation
The nitro (-NO$_2$) group, a potent electron-withdrawing entity (-I effect), enhances the carboxylate anion's stability. This increased stability renders O$_2$N–CH$_2$–COOH more acidic than CH$_3$–COOH. As greater acidity correlates with a lower pK$_a$, Assertion (A) is valid, and Reason (R) accurately substantiates it.
