Help on chemistry question ? please

I got the first two right, but i keep getting the bottom question wrong.
http://s122.beta.photobucket.com/user/jo…

Molarity HF = moles / L = 0.0450 / 1 L = 0.0450 M

PI = (i)(M)(R)(T)

i = PI / MRT = (1.26 atm) / (0.0450 moles/L)(0.0821 L atm / K mole)(302 K) = 1.13

The acid must be 13% ionized.