Explanation:

- Amplitude refers to the maximum extent of a vibration or oscillation, measured from the position of equilibrium. It is not the distance between successive particles in their paths.

- Wavelength is the correct term for the distance between two successive particles that are at exactly the same point in their paths and moving in the same direction. It is typically used in the context of wave motion, such as sound waves, light waves, or other periodic waves.

- Wavefront is a surface over which an oscillation has a constant phase. It's a concept used in wave propagation and does not describe the distance between particles.

- None of these would be selected if none of the options fit the description, but in this case, the right term is available.

Therefore, the correct answer is:

- Option 2: Wavelength