Comparing the stability of geminal diols Arrange the given gemdiols in decreasing order of their stability:


I thought that high angle strain would correspond to low stability, and therefore I compared the stability of the rings, which yields the answer as C &gt; B &gt; A, but, the answer given in my textbook is the opposite i.e., A &gt; B &gt; C.
On googling, I found out that, in this case, when the corresponding ketone hydrolyses to form the gemdiol then the one which gets greater relief of angle strain will have higher stability. But why do we have to check that? And I don't  know the reliability of the source. Moreover, what is wrong in my reasoning?
Your reasoning is correct, but I think you'd mistakenly compared the ring strain of the rings, while I would have compared the ring strain in the corresponding ketones.
Note that, you are asked about the stability of gem-diols, which could convert into the corresponding ketone. The point is, the ring isn't going to change, so the stability of rings don't matter.
Now, as you know the corresponding cyclic ketones would be $\ce{sp^2}$ hybridized. So, the ring angle should be $120^\circ$ in order to minimize the ring strain in ketone. The most closest is in C and least is in A.
Hence, the order.