What is a buffer?
a. an acid-base conjugate pair that changes the reaction rate
b. an acid-base conjugate pair that changes dissociation constants. c. an acid-base conjugate pair that precipitates out salts
d. an acid-base conjugate pair that keeps the ph from changing

D. An acid-base conjugate pair that keeps the pH from changing

Explanation: the answer is D. An acid-base conjugate pair that keeps the pH from changing, because we have to keep in mind which is the scope of this solution, and the scope is maintain the pH despite the changes in the solutions or support any change when you add another solution to the buffer.

also we need to know that a Buffer achieve their resistance to the changes of the pH, because of the presence of an equilibrium between the acid HA and its conjugate base.

This equilibrium give the properties to this solution to support the changes.

each chemical family is represented as a group or column on the periodic table. based on chemical properties, there are 6 types of chemical families. group 1 represents alkali metals, group 2 represents alkaline earth metals, groups 3 to 12 represent transition metals, groups 13 to 16 represent non-metals and other metals, group 17 represents halogens and group 18 represents noble gases.