Which is not a physical property?
a. hardness
b. boiling point
c. ability to conduct electricity
d. ability to combine with oxygen

The correct answer to the question is D). Ability to combine with oxygen.

EXPLANATION:

Before going to answer this question, first we have to understand physical and chemical change.

The change or reaction  is said to be physical if there will be no change in the chemical configuration of the substance. The property corresponding to this change is called physical property which won't change the configuration of the substance. It is measurable and simply denotes the physical states of a system.

A chemical change is a change in  which a new substance is formed due to the chemical reaction. Here, both the reactants and products have different chemical configuration. The property corresponding to it is called chemical property.

As per our questions, hardness, boiling and ability to conduct electricity are the physical properties of a substance.

The ability to combine with oxygen is not a physical property. It is so because it will result into the formation of a new compound.

Hence, the correct answer to the question is the ability to combine with oxygen.