QJEEM19Che694: JEE Main 2019 Chemistry - Class 11 JEEM19Che694 Solution: The correct decreasing order for acid strength is :

After releasing proton (H⁺) the more stable anion is more acidic nature. The 4 anions are $\to$



Here $-$ NO₂, $-$ CN, $-$ Cl, $-$ F all of them have $-$ I effective and all have same distance from the anion ( $-$ O ^$-$ ).

So depending on which one have more power $-$ I effect will be more stable.

Acidic nature $\propto$ $-$ I power.

$-$ I power order :

$-$ NO₂ > $-$ C $\equiv$ N > $-$ F > $-$ Cl

So, acidic strength order $\to$

NO₂ $-$ CH₂ $-$ COOH > NC $-$ CH₂ $-$ COOH
> F $-$ CH₂ $-$ COOH > Cl $-$ CH₂ $-$ COOH