Question

which among 2 chloro propanoic acid and 2 chloro butanoic acid is stronger
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Answer 1

Carboxylic acids (RCOOH) acidity is due related to the equilibrium shown below.

RCOOH = H+ + RCOO-

Anything that displaces the equilibrium to the right will result in increased acidity. In turn, this is related to the stability of RCOO-. Organic compounds tend to prefer being neutral but, if charged, then ways to distribute the charge are sought.

In the case of 2-chlorobutanoic acid 3-chlorobutanoic, they both bear chlorine, which is fairly electronegative. In hydrocarbons, chlorine will draw electron density toward it through induction, which occurs through bonds. The magnitude of the effect rapidly decreases with the number of intervening bonds. Therefore the effect of the chlorine on stabilizing RCOO- through induction will be greatest for the 2-chloro derivative, lesser for the 3-chloro (and yes, even less for the 4-chloro derivative).

So, this is the prediction. What are the numbers? I am going to include butanoic acid (no chlorines) and also the 4-chlorobutanoic acid derivative. Here are the pKas:

butanoic acid pKa = 4.76

2-chlorobutanoic acid pKa = 2.86

3-chlorobutanoic acid pKa = 4.05

4-chlorobutanoic acid pKa = 4.52

So, all three chlorobutanoic acids are stronger acids than butanoic acid though the acidity rapidly with the separation between the carboxylate and the chloro substituent.