Can you check my answer below, please?

Elizabeth did an experiment to test the effect of salt water on rusting rate of a nail. She put 3 nails in the same bowl of salt for one week. How could she improve her experiment?

Ans: 1) place each nail in a separate bowl with different amounts of water and salt
2) same as above but use different liquids, maybe?

Yes. I'd put 3 nails into plain water. Using other amounts of salt and other liquids would also improve the experiment.