Question

Methane can be decomposed into two simpler substances: hydrogen and carbon. Therefore, methane 1. is a gas. 2. cannot be an element. 3. must be a mixture. 4. must have the formula CH.

Answer 1

Answer: 2. cannot be an element.

Explanation:

Element is a pure substance which is composed of atoms of similar elements.It can not be decomposed into simpler constituents using chemical reactions.Example: Copper $Cu$

Compound is a pure substance which is made from atoms of different elements combined together in a fixed ratio by mass.It can be decomposed into simpler constituents using chemical reactions. Example: methane $CH_4$

$CH_4\rightarrow C+2H_2$

Thus as it can be decomposed into its constituent elements, it is a compound.

Mixture is a substance which has two or more components which do not combine chemically and do not have any fixed ratio in which they are present.

Thus methane cannot be an element.