Is potassium sulphate a base or acidic?

Potassium sulfate is neither base nor acid - it is a salt. You could get it by mixing something like potassium hydroxide (a base) with sulfuric acid and allowing the neutralization reaction to occur. Since it is actually often produce by reacting potassium chloride with sulfuric acid to get potassium sulfate and HCl (aka hydrogen chloride, aka hydrochloric acid when dissolved in water) you might expect it to be contaminated with some residual acid.