You have an empty 20 oz. soda bottle and you blow air over the opening to excite a fundamental standing wave. now, you slice off the bottom of the bottle (it’s plastic) without changing its length very much. you blow over the opening and excite a fundamental standing wave in the bottle with its bottom end open. the frequency of the standing wave in the second case:

The frequency of the standing wave in the second case is higher than that in the first case

Explanation:

The frequency and wavelength of a wave are related.

The moment you sliced the bottle, you've reduced the wavelength of the bottle.

When wavelength decreases, frequency increases and vice versa.

So, When frequency increases in the second case, more wave crests pass a fixed point each second. That means the wavelength shortens. So, as frequency increases, wavelength decreases. The opposite is also true—as frequency decreases, wavelength increases.