Activity co-efficient is a measure of the

Answer: Option A

Activity coefficient $${\gamma }_i=\frac{{\stackrel{⌢}{f_l}}^{real}}{\stackrel{⌢}{{f_l}^{ld}}}$$
For an ideal solution activity coefficient $$=1$$
And for real solution it tells about the departure from ideal solution by real solution like compressibility factor in case of gases.