Answer:
Wavelength
Step-by-step explanation:
A wave can be defined in terms of its frequency, wavelength, amplitude etc.
The distance between two corresponding parts of a wave, for example from crest to crest or trough to trough is called its wavelength.
It is represented by
.
The relation between frequency, speed of a wave and its wavelength is given by :

So, the correct option is (4) "wavelength".