Answer:
b.the distance in which an oscillation repeats itself.
Step-by-step explanation:
When a wave travels on the surface of water , the medium particle oscillates up and down remaining at the same place . They push their oscillation forward in the direction in which wave moves. wave length is distance between two consecutive oscillating particles having same phase of oscillation . When an oscillation repeats itself , they come to the same phase as the phase in the beginning.
Hence second option is correct.