The blue ball in the game of pool is the #2.
The ball that you intend to play.
The 8 ball
This is not possible in any common game of pool. Only Straight Pool allows the balls to be placed in nearly any position to accomplish this - no other common pool game allows placing the balls in that order. The middle of the rack is in between the second and third row of balls. It appears what is being asked is what ball will be in the 5th ball position, with one ball to left and one ball to the right if all the balls are arranged lowest to highest. This would be the 5 ball. However, Straight Pool requires that the 1 ball and the 5 ball be placed in the corners. Therefore, no pool game allows the balls to be placed in the way required - so, any ball may be in the "middle" position depending upon the game of pool being played.
eight ball
8
The fifth ball in a pool ball triangle will dpend upon the game being played. In Straight Pool, it can be any of 13 different balls. Only the 1 and the 5 cannot be located there. In 8 Ball, the 5th ball must be the 8 ball.
Pool
Pool
So you can tell which is the cue ball
That is lose of game.
If someone in a game of straight pool hits another person's ball and then hits the eight ball into the pocket, they do not win the game. In order to win in pool, you must be the first to get all of your balls into the pockets, and you must also get the eight ball into a pocket without touching another person's ball.