I think it's Chlorine but, not 100% sure. so C.
Answer: -
The rate decreases as the concentration of the reactants decreases
Explanation: -
A reaction involves change of the reactants into products.
Initially there is only reactants. So the rate if reaction is high.
After some time there are products. So the amount of reactant is less.
Reactions involve collisions of reactant molecules. As the reactant amount decreases, collisions between the reactants decreases. As such the rate of reaction decreases with the progress of the reaction.
The answer would be the last one- it separates dissolved substances.
Have a great rest of your day!
Because they’re both made up of two substances that are not chemically combined