44 given the balanced ionic equation:
3pb2+ + 2cr ==> 3pb + 2cr3+
what is the number of moles of electrons gained by 3.0 moles of lead ions?
(1) 5.0 mol (3) 3.0 mol
(2) 2.0 mol (4) 6.0mol
i know that the answer is 4 i just need an explanation of how

Astudent pours 10.0 g of salt into a container of water and observes the amount of time it takes for the salt to dissolve. she then repeats the process using the same amounts of salt and water but this time she slowly stirs the mixture while it is dissolving. the student performs the experiment one more time but this time she stirs the mixture rapidly. the dependent variable in this experiment is: time for salt to dissolve speed of stirring amount of water mass of salt