What is the change in the serum Potassium (K+) level in acidosis & alkalosis?

The change in both are opposite to each other.

Acidosis - ↑ K+ level            &                Alkalosis - ↓K+ level

You can remember it as:

Alkalosis = al-K-a-LOW-sis i.e. in alkalosis the K+ level in serum is low. The opposite will happen in acidosis i.e. high K+ level.