Why fluoroform is less acidic than chloroform..?

While comparing two compounds for acidic strength, we can check for the stability of their conjugate bases. The one having the most stable (weak) conjugate base is the strong acid.

The conjugate bases of Chloroform and Fluoroform are -CCl3 and -CF3 respectively.

The negative charge in -CF3 is stabilized by the inductive effect of the electronegative fluorine atoms while the negative charge in -CCl3 is stabilized by the resonance effect in which the negative charge is delocalized in the vacant d-orbitals of Cl atoms. F can’t stabilize the negative charge by resonance effect as it does not have d-orbitals. Resonance effect stabilizes charges much better than inductive effect as inductive effect operated through sigma bonds, electron density of which is difficult to perturb, while resonance effect operates through the labile pi bonds and lone pairs. So, -CCl3 is more stable than -CF3 .

Based on the above argument we can conclude that Chloroform is a stronger acid than Fluoroform.