Just eliminate them:
72 = 8*9 = 2*4*9 - this one actually has two squares as divisors, 4 and 9
42 = 2*3*7 - no squares here, so you stop and pick B.

If you want, we can go on. However, I don't recommend you do this on your exam. You need to try and save as much time as possible.

32 = 2*16 = 16 is the square of 4
25 is the square of 5, so it is obviously divisible by a square
12 = 3*4 - 4 is the square of 2

So the OA is ok.

thankyou Danaj