Answer:
Wavelength = the distance between two adjacent peaks of the wave.
Step-by-step explanation:
The wavelength of a wave is defined as the distance between two adjacent peaks of the wave or it is defined as the distance between two consecutive crests and troughs. It is denoted by
. Its SI unit is meters.
The relation between the frequency and the wavelength is given by :

Where
v is the speed
So, the correct option is (a). " the distance between two adjacent peaks of the wave".