[Fish200398]

1. FCH_2CH_2COOH
2. ClCH_2CH_2COOH
3. BrCH_2CH_2COOH
4. CH_3CHFCOOH

i think all of the compounds are acid. And i think the differences is the halogen attached to carbocylic acid. While all i know in HF HBr HCl, HF is the weakest due to strong electronegativity of  F makes it hard to give proton and HBr is the strongest due to larger radius. but what about this 4 acids what is the series strongest to weakest?

[AWK]

Most of organic acids are classified as weak ones.  You can check K_a (or pK_a)

[Fish200398]

there is no given Ka, maybe there are other ways to decide it

[Humr]

All are acids and last with nearest F to COOH group is strongest i think. And its because pulling eway electrons from H due to induction effect.

[AWK]

https://www2.chemistry.msu.edu/faculty/reusch/VirtTxtJml/crbacid1.htm

[hollytara]

Ka or Acid Strength 4>1>2>3

pKa is reversed.

F is most electronegative and is most effective at making acid stronger. 
4 has F one atom closer to acid group and therefore also more effective.

[Fish200398]

in HF HBr HCl HF the series are HBr > HCl > HF. but now in this question the series reverse into F>Cl>Br, why?

[AWK]

https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Supplemental_Modules_(Inorganic_Chemistry)/Descriptive_Chemistry/Elements_Organized_by_Block/2_p-Block_Elements/Group_17%3A_The_Halogens/1Group_17%3A_General_Reactions/The_Acidity_of_the_Hydrogen_Halides

[Fish200398]

thanks all