What effect do impurities have on the crystal lattice? Why does that result in the lowering of the melting point of a solid?

It reduces the melting point due to a defect in the arrangement of the crystal lattice.

Explanation:

The presence of impurities creates a disorderliness in the uniformity of the crystal structure. It lowers the melting point by a few degrees because it becomes easier to overcome the intermolecular force of attraction.

It makes the array of crystals disordered.  

Lattice is a long chain three-dimensional arrangement of the molecules, atoms or ions in a crystal structure.

most of them using statistics and defining how things are being measured

the answer is f1 and d2 because if you put equal force on those two points the beam would balance trust me on this