What name is given to substances that resist changes in ph?

These are buffer systems (solutions of substances) with a steady concentration of hydrogenium ions. At addition to such solution of a small amount of acid or alkali does not change рН.
For example:
CH₃COOH + CH₃COONa    acetate buffer
KH₂PO₄ + K₂HPO₄  potassium phosphate buffer

If you open the bottle of perfume then nothing but the smell will come out of it and yes it is a type of gas smell because it’s say it in english so i can understand better and you