Water is a compound because it a. cannot be broken down into simpler substances. b. always has two hydrogen atoms for each oxygen atom. c. is made of water atoms joined together. d. both a and b

Option (B) is the correct answer.

Explanation:

A compound is defined as a substance in which two or more different elements in a fixed ratio by mass combine chemically with each other.

For example, chemical formula of water is and it is a compound because here two atoms of hydrogen chemically combine with one atom of oxygen.

And, the ratio of these atoms is 2 : 1. A compound can be broken down into simpler substance by chemical means only.

Whereas an element is a substance that contains only same type of atoms that cannot be broken down into simpler substances.

Thus, we can conclude that water is a compound because it always has two hydrogen atoms for each oxygen atom.

3. dark matter

empty space could also be a simple vacuum