Urgent: how is a pure substance different from a mixture?
a. pure substances are separated by physical means
b. mixtures are made up of more than one component
c. a pure substance is heterogeneous
d. mixtures cannot be separated by physical means.

Option (B) is the correct answer.

Explanation:

A pure substance is defined as the substance that contains either same or different type of atoms that are chemically combined to each other in a fixed ratio by mass.

For example, both and are pure substances.

A pure substance can only be separated by chemical means.

Whereas a mixture is defined as the substance that contains two or more different number of substances that are physically mixed together.

For example, salt in water is a mixture.

In a mixture, solute particles can be either evenly or unevenly distributed in the solvent.

A mixture will always be separated by only physical means.

Thus, we can conclude that a pure substance different from a mixture as mixtures are made up of more than one component.

radioactive decay occurs in unstable atomic nuclei – that is, ones that don't have enough binding energy to hold

the nucleus together due to an excess of either protons or neutrons.