The strongest interparticle attractions exist between particles of a and the weakest interparticle attractions exist between particles of a

The correct terms to fill in the blanks are solid and gas. The strongest interparticle attractions exist between particles of a solid and the weakest interparticle attractions exist between particles of gas. In a solid substance, the atoms are very close to each other and collision frequency is very high, Thus, attraction between particles is high. For a gas, the molecules are very far from each other to the point that they do not collide. Collision frequency is very small for a gas leading to a weak attraction between particles. An intermediate phase of these two is called the liquid phase, where the particles are far apart but not that far where collisions are more likely to happen.

Pe = 1/2k(x)^2  and .05n/m = .05x10^-9m = x