#### Answer

We can rank the blocks in order of the buoyant force on them, from largest to smallest:
$c = d \gt a = b \gt e = f$

#### Work Step by Step

If a block is floating in water, then the forces are in equilibrium. That is, the buoyant force is equal in magnitude to the weight of the block. We can find the buoyant force on each block.
(a) $F_b = mg = (0.020~kg)(9.80~m/s^2) = 0.196~N$
(b) $F_b = mg = (0.020~kg)(9.80~m/s^2) = 0.196~N$
(c) $F_b = mg = (0.025~kg)(9.80~m/s^2) = 0.245~N$
(d) $F_b = mg = (0.025~kg)(9.80~m/s^2) = 0.245~N$
(e) $F_b = mg = (0.010~kg)(9.80~m/s^2) = 0.098~N$
(f) $F_b = mg = (0.010~kg)(9.80~m/s^2) = 0.098~N$
We can rank the blocks in order of the buoyant force on them, from largest to smallest:
$c = d \gt a = b \gt e = f$