Question

co₂, carbon dioxide on the right). what is one difference you notice with the visual model in slide 2? ( in terms of combination of atoms/elements)
h₂o - how many types of colored spheres? -
co₂ - how many types of colored spheres ?

Explanation:

Step1: Analyze $H_2O$

The chemical formula $H_2O$ has two elements, hydrogen ($H$) and oxygen ($O$). In a visual - model represented by colored spheres, there would be 2 types of colored spheres.

Step2: Analyze $CO_2$

The chemical formula $CO_2$ has two elements, carbon ($C$) and oxygen ($O$). In a visual - model represented by colored spheres, there would be 2 types of colored spheres. But if we consider the ratio of atoms, in $H_2O$ there are 2 hydrogen atoms for every 1 oxygen atom, while in $CO_2$ there is 1 carbon atom for every 2 oxygen atoms. In terms of the combination of atoms/elements, one difference could be the ratio of the non - oxygen atoms to oxygen atoms. Also, the elements involved are different ($H$ in $H_2O$ and $C$ in $CO_2$).
For the number of types of colored spheres:
For $H_2O$: 2
For $CO_2$: 2

Answer:

For the difference in combination of atoms/elements: In $H_2O$, hydrogen and oxygen combine in a 2:1 ratio of $H$ to $O$, while in $CO_2$, carbon and oxygen combine in a 1:2 ratio of $C$ to $O$ and the elements involved are different ($H$ vs $C$).
For $H_2O$: 2
For $CO_2$: 2