Which type of matter is composed or two or more elements that are chemically combined in a fixed proportion?

Hello.

When dealing with two or more elements in a fixed proportion, your answer is going to be "B.) Compound." The explanation is pretty basic when you narrow it down - think of it like the English version of a compound sentence; there are two independent clauses that have related ideas (such as this one, for example).

Let's use an example of a compound element, such as , or Water.
This is a compound element that is composed of the two elements "Hydrogen" and "Oxygen" - for every 2 Hydrogen atoms there is one Oxygen atom.

I hope this helps!

30litre of li2o is 1.0002mole approximately 1 mole