Answer:
The distance between successive crests decreases.
Step-by-step explanation:
If f is the frequency and
is the wavelength of a wave, then the speed of the wave is given by :

on rearranging,

We know that wavelength of a wave is equal to the distance between successive crests or troughs.
If the frequency of a wave increases while its speed remains constant, the wavelength decreases i.e. the distance between successive crests decreases.