A substance is considered acid when it either give a H+ as disolving or takes an OH-. On the other hand a substance is considered basic when it give an OH- or takes a H+. Like HF is an acid (H+, F-) and NaOH is basic (Na+, OH-). For KNO2, it can take an H+ to go back to HNO2, so it is basic.

Is KNO3 strong or weak?

Potassium Nitrate is a crystalline salt, KNO3; a strong oxidizer used especially in making gunpowder, as a fertilizer, and in medicine.

Is potassium nitrite a strong base?

-) is a significant Brønsted base and reacts with water in a hydrolysis reaction: The hydrolysis reaction above produces hydroxide ions, thus the solution of the salt potassium nitrite will be basic.