# Arranging different oxygen-containing organic compounds by decreasing acidity

I am facing difficulty in the following problem.

Arrange the following compound in decreasing order of acidity.

It is clear that conjugate base of (Q) is more stable.hence it is most acidic.in R) there is much steric hinderence so my view is that it should be less acidic.however I am not sure about it.

And this is the type of question for which Professor Mayr made us chemistry students rote memorise typical $\mathrm{p}K_\mathrm{a}$ values. Here are some.
Therefore, the order is $\mathrm{Q > P > R > S}$