Can someone help me out please?

2

Explanation:

You're dealing with ammonium carbonate,  

(

NH

4

)

2

CO

3

, an ionic compound made up of ammonium cations,  

NH

+

4

, and carbonate anions,  

CO

2

−

3

.

Now, it's important to realize that in order for ammonium carbonate to be neutral, you need the overall positive charge of the cation to balance the overall negative charge of the anion.

This is what that  

2

subscript denotes - the  

1

+

charge of the ammonium cation tells you that you need two such cations in order to balance out the  

2

−

charge of the carbonate anion.

Since one ammonium cation contains

one nitrogen atom,  

1

×

N

four hydrogen atoms,  

4

×

H

it follows that two ammonium cations will contain

two nitrogen atoms

eight hydrogen atoms

Therefore, one formula unit of ammonium carbonate will contain two atoms of nitrogen, one from each ammonium cation.

what experimental evidence led scientists to change from the previous model to this one?

a few of the positive particles aimed at a gold foil seemed to bounce back.

the colors of light emitted from heated atoms had very specific energies.

experiments with water vapor showed that elements combine in specific proportions.

cathode rays were bent in the same way whenever a magnet was brought near them.