Explain how the presence of several oxygen atoms ina compound containing an-OH group can make the compound acidic.

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.