Pleas check the following for me...

Question

"A drop of oil (vol 0.051cm ) is released on to the surface of a pond where it covesr an area of 40cm2. Assume that the oil film has a uniform thickness equal to the diameter of an oil molecule. Calculate the diameter of an oil molecule & express your answer in sn to an approp. sf."

Is the answer of "1.275 x 10^-3 MM" correct? (note i converted figs to mm)

Have you made an error in decimal point. I have 0.001275 cm which doesn't convert to your answer in mm. I would use mm for millimeters. In addition, I question the number of significant figures and the problem specificially states
"to an approp. sf". I don't know what the sn in your original post stands for. Anyway, you have two significant figures in the 40 cm^2 AND in the 0.051 cm^3 so you can have no more than 2 s.f. in the answer. That means 0.001275 cm rounds to 0.0013 cm or 1.3 x 10^-3 cm.
Check my work.