What would be the proper way to write the formula for a compound containing barium and nitrogen?

The conventional equilibrium constant expression (kc) for the system below is: 2icl(s) ⇄ i2(s) + cl2(g) [cl2] ([i2] + [cl2])/2[icl] [i2][cl2]/[icl]2 none of the listed answers are correct [i2][cl2]/2[icl]

What is the percent by mass of oxygen in fe2o3

Which change to the system wood cause the freely-moving piston to lower?