A quick way to identify a comminution law is to ask what quantity the energy is said to be proportional to. Rittinger's law ties energy to the newly created surface area (a difference of \(1/d\) terms), Bond's law ties it to the difference of \(1/\sqrt{d}\) terms based on crack propagation theory, and Fick's law is not a size-reduction law at all, it governs diffusive mass transport and has no particle-size term in this form. Kick's law is the one comminution law that states energy is proportional to the ratio of the initial and final sizes expressed as a natural logarithm, exactly the \(\ln(d_1/d_2)\) form seen in the given equation.
Therefore, the correct answer is Kick's law.