(i) For more acidic character, we need an electron-withdrawing factor which will stabilizing the anion formed after loss of proton. In this case, the second compound will be more acidic than the first as the second compound has an sp2 hybridized adjacent carbon and it is more electron withdrawing than an sp3 hybridized one.
(ii) In this case, the 1st compound will be more acidic as the anion here is stabilized by the phenyl ring. There is no such factor in 2nd compound.
(iii) The −OH group in second compound shows stronger −I effect due to which it becomes more acidic than first compound, having no such group.