Classify the following groups as electron-withdrawing ($-I$ effect) or electron-donating ($+I$ effect) inductive effect groups: $-CH_3, -Cl, -NO_2, -(CH_3)_3C, -OC_6H_5, -C_6H_5, -OH, -NH_2, -CH_2CH_3$.

(N/A) The inductive effect is the permanent displacement of sigma electrons along a carbon chain due to the difference in electronegativity of the atoms or groups attached.
$1$. Electron-withdrawing groups ($-I$ effect): These groups attract electrons towards themselves. Examples: $-Cl, -NO_2, -OC_6H_5, -C_6H_5, -OH, -NH_2$.
$2$. Electron-donating groups ($+I$ effect): These groups release electrons away from themselves. Examples: $-CH_3, -(CH_3)_3C, -CH_2CH_3$.