Answer: Frequency
Explanation:
Wavelength is defined as the distance between two crests or two troughs in a wave. It is measured in meters.
Frequency is defined as the number of oscillations happening in a given amount of time. It is measured in Hertz.
Intensity is defined as the power delivered per unit area.
Amplitude is defined as the maximum displacement of a particle from its rest position. It is also measured in meters.
Hence, if the number of troughs are increasing in a given time, the oscillations increase, the frequency is increased.