Due to stronger–I-effect of F than that of Cl, CHF3 should be more acidic than CHCl3. But actually reverse is true. This is due to : CCl3− left after the removal of a proton from CHCl3 is stabilised due to presence of d-orbitals in Cl than: CF3− left after the removal of a proton from CHF3 which is not stabilised due to the absence of d-orbitals on F.