(N/A) Inductive effect: The permanent displacement of sigma ( $\sigma$ ) electrons along a saturated chain,whenever an electron-withdrawing or electron-donating group is present,is called the inductive effect. The inductive effect can be $+I$ effect or $-I$ effect.
$-I$ effect: When an atom or group attracts electrons towards itself more strongly than hydrogen,it is said to possess $-I$ effect. Example: $F \leftarrow CH_2 \leftarrow CH_2 \leftarrow CH_2 \leftarrow CH_3$.
$+I$ effect: When an atom or group attracts electrons towards itself less strongly than hydrogen,it is said to possess $+I$ effect. Example: $CH_3$ $\rightarrow CH_2$ $\rightarrow Cl$.
Electromeric effect: It involves the complete transfer of the shared pair of $\pi$ electrons to either of the two atoms linked by multiple bonds in the presence of an attacking agent. It is a temporary effect.
$(a)$ $Cl_3CCOOH > Cl_2CHCOOH > ClCH_2COOH$: The order of acidity is explained by the Inductive effect ($-I$ effect). As the number of chlorine atoms increases,the $-I$ effect increases,which stabilizes the carboxylate anion and increases acid strength.
$(b)$ $CH_3CH_2COOH > (CH_3)_2CHCOOH > (CH_3)_3C \cdot COOH$: The order of acidity is explained by the Inductive effect ($+I$ effect). As the number of alkyl groups increases,the $+I$ effect increases,which destabilizes the carboxylate anion and decreases acid strength.