In each case, the same bond gets broken - the bond between the hydrogen and oxygen in an -OH group. Writing the rest of the molecule as "X"
The factors to consider
Two of the factors which influence the ionisation of an acid are:
the strength of the bond being broken,the stability of the ions being formed.In these cases, you seem to be breaking the same oxygen-hydrogen bond each time, and so you might expect the strengths to be similar.
