Arrange the following acids in decreasing order of [H+] concentration
(a)I>II>III   (b)II>III>I    (c) III>II>I

More electron withdrawing groups more is the acidity.If we check here alpha carbon of third molecule is bonded to sp3 carbon which is less electron withdrawing  then  sp2 carbon in second and third structure.In first structure there is a ring  which can act as better electron withdrawing then second structure.
order must be
I> II> III