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

Low tide is the state of the tide when at its lowest level

Tides are the alternate rising and falling of the sea, usually twice in each lunar day at a particular place, due to the attraction of the moon and sun

High tide is the state of the tide when at its highest level

so the answer is most likely High Tides