"Which metals tend to be stronger, those that form FCC or those that form BCC crystals? " This is the solution provided which doesn't make much sense to me: "You should look at APF and coordination number of each crystal system to base your answer" Is this even a valid question? Doesn't the answer depend on which direction the material is going to be subjected to a force since "strongness" is a directional property? I thought we should choose a particular direction for both systems and look at planar and linear densities. Hence, the slip phenomenon in the crystal structure with a greater planar density in the "chosen direction" will progress with more ease which suggests that the the material is "stronger" if subjected to a force in the chosen direction. I would appreciate it if someone could point me to the flaw in my reasoning.