A100 hz sound wave is traveling through the air. if we increase the frequency to 200 hz, this will the wavelength. a 100 hz sound wave is traveling through the air. if we increase the frequency to 200 hz, this will the wavelength. increase decrease not change

The correct answer is "decrease":
A 100 hz sound wave is traveling through the air. if we increase the frequency to 200 hz, this will INCREASE the wavelength.

Let's see why. The basic relationship between frequency and wavelength of a wave is

where
v is the speed of the wave
f its frequency
its wavelength

We can see from this equation that, if the frequency is increased, if the speed of the wave does not change (and this is the case), then the wavelength of the wave must decrease, since the ratio  becomes smaller.