In a the substances retain their individual chemical and physical properties.

Explanation:

A mixture is defined as a substance in which two or more solutes are added in a solvent. Particles of a mixture never combine chemically with each other.

A stable mixture is defined as a mixture in which solute particles do not settle. Basically, in a stable mixture particles remain their individual properties.

And, when two substances chemically combine to each other then it leads to the formation of a compound or molecule whose chemical properties are different from its reactants.

Therefore, we can conclude that in a mixture, the substances retain their individual chemical and physical properties.

the answer is a and have a great day