Which substance can not be broken down by a

chemical change?

(1) ethane (3) silicon

(2) propanone (4) water

 (3) silicon

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: Silicon (Si)

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: ethane , propanone and water

answer: c.

explanation:

"the periodic table is arranged in order of atomic number."