The pka of a compound whose acidic or basic form absorbs uv or visible light can be determined spectroscopically since

It seems that you have missed the necessary options for us to answer this question so I had to look for it. Anyway, here is the answer. The pka of a compound whose acidic or basic form absorbs uv or visible light can be determined spectroscopically since  the pK a is the same as the pH at which half of the total absorbance increase occurs. Hope this helps.

The teacher is mostly talking about the distillation of a mixture