Most acidic one is

From 1 to 2EWG increases the acidic strength of acid by increasing the stability of corresponding conjugate base,hence 2 is more acidic than 1.FROM 2 TO 3 As the  number of EWG'S increases,acidic strength also increases,due to increases in the stability of conjugate base.FROM 3 TO 4With decrease in the distance between the EWG and N—H [Acidic hydrogen containing group] group,the acidic strength increases due to increase in the stability of conjugate base.