Hydrolysis of a compound  X at PH=5, proceeds with half life of 600 minutes  for any concentrations of X, . However at pH = 6, the half life changes to 60 minutes, The rate law expression for hydrolysis possibly can be

At pH = 5 the t12∝ [X]0  means the reaction is first order w.r.t X because t12  remains same for any  conc. of X so rate  = k[X]1    [H+]n   [n=order w.r.t H+ion] Also t12  for [H+]∝1[C0]n−1or  ∝  C01−n ∴   600∝  [10−5]1−n  and       60∝  [10−6]1−n or 10=(10)1−n  or  1−n=1 and n = 0