Question

Which of the following is a polyatomic ion: CH3COOH, CR2O7^2-, Na^+, or H2?

Answer 1

`[Cr_2O_7]^(2-)` is a polyatomic ion.

Explanation:

Polyatomic ions are ions with charge that are made up of two or more atoms.

For example:

• `[H_3O]^+`
• `[SO_4]^(2-)`
• `[CO_3]^(2-)`

Notice that all of these examples have a charge attached to them. This is what makes them ionic.

Also, all of these ions are made up of more than 2 ions.

Looking through the problem that was given, we have 4 different choices.

First, discard the ones that do not have a charge attached to them. `H^2 and CH_3COOH` do not have charges associated with them, so discard that.

Second, discard the ones that do not have two or more ions in them. `Na^+` is a single sodium ion, so this can be discarded.

Finally, you are left with the last choice: `[Cr_2O_7]^(2-)`. This is your answer.