An Atom is the basic building parts of everything a ion is a <span>molecule with a net electric charge and a isotope is energy ball of different number of protons and neutrons in the nuclei</span>
A substitution is a mutation that exchanges one base for another. This can include a change in a single chemical letter. ex. changing a to g or in your case g to a. I believe the correct answer should be B.
In short a physical change is something that changed the way something looks but doesn't affect the chemical makeup. Drying your hair doesn't change the color of your hair, it just makes it dry so thats a physical change. Rust forming on a knife is a chemical change becaause the water reacts with the chemical makeup of the knife. Hope that helps.
X, Y, and Z are elements.
An element is the smallest part of a substance that can exist on its own and can not be broken down into smaller unit.
From the question, W was broken down to give X, Y, Z. All three substances can not be broken down by chemical means.
The fact that X, Y and Z can not be broken down by chemical means implies that they are elements.
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