Which of the following exhibits - I effect?

The inductive effect refers to the polarization of a $\sigma$-bond due to the electron-withdrawing or electron-donating nature of adjacent groups or atoms.

Groups that withdraw electrons more strongly than hydrogen exhibit a $-$I effect, while groups that donate electrons more strongly than hydrogen exhibit a $+$I effect.

Alkyl groups such as $-\text{CH}_3$, $-\text{C}_2\text{H}_5$, and $-\text{C}(\text{CH}_3)_3$ are electron-donating and show a $+$I effect.

The $-\text{NO}_2$ group contains highly electronegative oxygen and nitrogen atoms, making it a strong electron-withdrawing group. Therefore, it exhibits a strong $-$I effect.

Answer: $-\text{NO}_2$