The time required for molecules in a solution to move from a to b is proportional to the square of the distance from a to b. what property of diffusion does this principle explain?

Diffusion is rapid for short distances but slow for long distances

Explanation:

Let's call t the time required for molecules in a solution to move from a to b, and d the distance between a and b. For what the sentence says

t ∝ √d where ∝ means proportional.

So, as the distance increases, the time of diffusion increases too, and the process is slow. So, diffusion is rapid for short distances but slow for long distances.

answer is: c. the experiment shows that the red substance experienced a chemical change.

this is chemical change (chemical reaction), because two new substances are formed (metalig liquid and gas), the atoms are rearranged and the reaction is followed by an energy change.

this is example of chemical decomposition.

chemical decomposition (analysis) is the separation of a single chemical compound into its two or more elemental parts or to simpler compounds.  

chemical decomposition is opposite of chemical synthesis.

1.solid

2.carbon dioxide

3.helium