Final answer:
James uses 50 pails of water to fill the fish tank.
Step-by-step explanation:
To find out how many pails of water James uses to fill the fish tank, we need to divide the total capacity of the tank by the capacity of each pail. The fish tank has a capacity of 100 liters and each pail can hold 2 liters of water. So, to find the number of pails, we divide 100 by 2, which equals 50 pails.