What is the osmotic pressure of .100 M solution of aluminum chloride at 27 deg C?

I used the formula:
pi=(i)(M)(R)(T)
wasn't sure what i was but for M put down 0.100M, R=0.08206 and T=300K
Answer is 9.85, but not sure how to get that.

What did you substitute for i? For AlCl3 you should have substituted 4.

4*0.08206*300*0.1 = 9.847 which rounds to 9.85 atm.