As the frequency of a wave decreases, the wave's -
period decreases
speed decreases
wavelength increases
amplitude increases

Wavelength increases.

Explanation:

The Speed of a wave is given by the product of its frequency and wavelength.

i.e ν = fλ, where ν is the wave speed, f is the wave's frequency, and λ is the wavelength.

So for the speed to have a constant value at an instance, then if the frequency decreases, the wavelength will increase and vice versa.

h let me think