Solution

Inductive effect is the displacement of sigma electrons towards more electronegative species. It is transmuted though a chain of C atoms. It is classified into +I effect and -I effect.
Electron releasing groups such as alkyl groups show +I effect. -I effect is shown by electron withdrawing groups such as nitro, cyano, halo, amino etc.

Electromeric effect is temporary effect and involves transfer of pi electrons by the demand of attacking reagents towards more electronegative species.It is more powerful than inductive effect and is shown by compounds having C=C, C=N or $$N \equiv N$$ groups. It is classified into + E effect and -E effect.
In +E effect, pi electrons are transferred towards the attacking reagent whereas in -E effect, pi electrons are transferred away from the attacking reagent.

The decreasing order of the acidity $$\displaystyle Cl_3CCOOH> Cl_2CHCOOH> ClCH_2COOH $$ is explained on the following basis.
Electron withdrawing groups such as Cl, disperses the negative charge over the molecule and increases its stability and acidic nature. Hence, more is the number of electron withdrawing groups, more is the acidic nature.