Answer:
1) Concentration
Step-by-step explanation:
In general, the higher the concentration of a reaction, the faster the rate of the reaction will be.
Please keep in mind this is referring to the initial reaction rate and not a reaction that is at equilibrium.
You can also reason (intuit) this out:
For the reaction to occur, the molecules (in this case reactants) must collide with each other. The more molecules you have in a given space (volume) the more likely the odds are that the molecules will collide and react.
So, if you increase the concentration, you'll increase the odds of collision and in turn the rate of the reaction.
If you increase the VOLUME, it will have the opposite affect. You're giving the molecules more space and decreasing the concentration. So, the rate would decrease.
Increasing the amount of solution doesn't really change anything. The molecules still have the same concentration.
Increasing mass is vague. Does that mean the over all mass? Do they mean increase the mass of everything (solvent, reactants)? We don't know...
Concentration is the right answer.