Which of the following was not an attempt to form a union and organize workers in the late 1800s?
1- american federation of labor
2-american railway union
3-knights of labor
4-haymarket organization of workers

The correct answer is 4.

The name Haymarket is closely connected to labor movements in the US because of the very important riots that took place in the Haymarket square in Chicago in 1886, but was not the name of a union or a labor organization.

The Haymarket Riots took place after a bombing that occurred during a demonstration of workers, who were on strike, claiming for the 8-hours working day and also claiming against violence in the repression of the strike, that had been performed by the police.