Higher the stability of conjugate base higher is the acidity. the conjugate base of ethanol is the weakest because the + I effect of the ethyl group increases electron density upon oxygen atom which is already having an extra electron thus destabilizing it the most. in case of C6H5COOH the phenyl group is insulated so it exerts only -I effect on the resonance hybrid of carboxyl group stabilizing it by withdrawing electron density due tohigher electronegativity of sp2 hybridised carbon atom than sp3 hybridised -CH2-. But fluorine and chlorine are much more electronegative than carbon. and elecronegativity of fluorine is much more than that of chlorine. so -I effect follows the order of -F>-Cl>-Ph. so the stability of the conjugate follows the order of FCH2COO->ClCOO->PhCH2COO- . Hence the acidic strength of the corresponding acids follow the same order. thus in the decreasing order of the acid strength the order is FCH2COOH>ClCH2COOH>PhCH2COOH>EtOH