Answer: Option (a) is the correct answer.
Explanation:
When an element chemically combines with another element in a fixed ratio by mass then it results into the formation of a compound.
A compound can be separated into its constituent particles only by chemical means and not by any physical means.
An element is a substance which contains only one type or kind of atoms.
For example, a piece of sodium will contain only atoms of sodium.
An element cannot be divided into its constituent particles by any means.
Whereas particles of a mixture never combine chemically with each other. So, they can be separated by physical means.
Thus, we can conclude that if matter is uniform throughout and cannot be separated into other substances by physical means, it is a compound.
