Bob can use a process called precipitation to determine which solution is which. He can start by adding a small amount of each metal to each of the salt solutions, and then observe which combination produces a solid precipitate.
For example, if Bob adds magnesium to one of the solutions and a solid precipitate forms, he can conclude that the solution contains magnesium chloride. He can repeat this process with the other metals until he has identified all three solutions.
It is important to note that Bob should only add a small amount of metal to each solution, as adding too much can cause the reaction to become violent or produce dangerous gases. Additionally, Bob should wear appropriate safety equipment, such as gloves and goggles, when conducting this experiment.