The correct answer is option 2: Solid < Liquid < Gas.

Compressibility is a measure of how easily a substance can be compressed or squeezed into a smaller volume. In solids, the particles are tightly packed together and have very little space to move, making them less compressible. Therefore, solids have the lowest compressibility among the three states of matter.

In liquids, the particles are not as tightly packed as in solids, allowing them to move past each other more freely. Although liquids are more compressible than solids, they still have a relatively low compressibility compared to gases.

Gases have particles that are more spread out and have a lot of space between them. This allows gas particles to move freely and easily compress when subjected to pressure. Therefore, gases have the highest compressibility among the three states of matter.

To summarize, the correct order of compressibility is: Solid < Liquid < Gas.