A young woman slashed a stranger during an argument over a subway seat on a Harlem train, police said Wednesday. Christena Chambers, 19, was riding a No. 6 train when she got into an argument over an available seat with the 52-year-old victim about 3:20 p.m. Tuesday, cops said. The two continued to argue as the train pulled into the 125th St. station. They got into a match as they exited the subway car onto the platform, cops said. As the tussle escalated, Chambers allegedly pulled a knife and struck the older man on the side of the face, slicing his earlobe, cops said. Chambers tried to run off but was grabbed by cops responding to the scene, police said. Cops charged Chambers with assault, weapon possession and harassment. She lives in Crotona Park East section of the Bronx, according to cops. Her arraignment in Manhattan Criminal Court was pending Wednesday. Her victim was treated at the scene. There has been a 3% drop in assaults in the city’s subway system so far this year compared to last year. As of Sunday, cops were investigating 474 assaults compared to 493 by this time last year.